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Petroleum Experts

User Manual

IPM GAP Version 8.5 February 2011

GAP IPM - Multiphase Production Optimisation OVERVIEW by Petroleum Experts Limited

GAP is a multiphase optimiser of the surface network which links with PROSPER and MBAL to model entire reservoir and productions systems. GAP can model production systems containing oil, gas and condensate, in addition to gas or water injection systems. GAP has the most powerful and fastest optimisation engine in the industry. Wellhead chokes can be set, compressors and pumps optimised, and Gas for gas lifted wells, allocated to maximise Oil Production or Revenue while honouring constraints at any level. With MBAL field production forecast can be run. GAP is part of the IPM suite, which allows the engineer to build complete system models, including the reservoirs, wells and surface system.

APPLICATIONS • Full field surface network design • Field Optimisation studies with mixed systems (ESP, GL, Naturally Flowing) • Multi-phase Looped Network Optimisation • Advises on wellhead chokes settings to meet reservoir management targets • Field Gas Lift Optimisation • Models full field injection system performance, using MBAL reservoir tank models • Compressor and Pump system modelling • Production forecasting • Programmable elements • Rigorous Compositional modeling from the Reservoir to the Process side • Fast and robust Optimisation algorithm using Sequential Quadratic Programming SQP • Easy to use graphical interface for drawing system network (using icons for separators, compressors, pipelines, manifolds and wells, inline chokes and reservoir tanks) • GAP is unique in being able to model, optimise and run predictions of the entire production system, with MBAL and PROSPER • Naturally flowing, gas lift and ESP wells can all be included in the same production system model • GAP links to PROSPER (well model) and MBAL (tank model) to allow entire production systems to be modelled and optimised over the life of the field • GAP optimisation technique is much more robust than iterative methods and is simpler to use.

3

Copyright Notice The copyright in this manual and the associated computer program are the property of Petroleum Experts Ltd. All rights reserved. Both, this manual and the computer program have been provided pursuant to a Licence Agreement containing restriction of use. No part of this manual may be reproduced, transmitted, transcribed, stored in a retrieval system, or translated into any language, in any form or by any means, electronic, mechanical, magnetic, optical or otherwise, or disclose to third parties without prior written consent from Petroleum Experts Ltd., Petex House, 10 Logie Mill, Edinburgh, EH7 4HG, Scotland, UK. © Petroleum Experts Ltd. All rights reserved. IPM Suite, GAP, PROSPER, MBAL, PVTP, REVEAL, RESOLVE, IFM and OpenServer are trademarks of Petroleum Experts Ltd. Microsoft (Windows), Windows (2000) and Windows (XP) are registered trademarks of the Microsoft Corporation The software described in this manual is furnished under a licence agreement. The software may be used or copied only in accordance with the terms of the agreement. It is against the law to copy the software on any medium except as specifically allowed in the license agreement. No part of this documentation may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or information storage and retrieval systems for any purpose other than the purchaser's personal use, unless express written consent has been given by Petroleum Experts Limited.

Address: Petroleum Experts Limited Petex House 10 Logie Mill Edinburgh, Scotland EH7 4HG Tel : (44 131) 474 7030 Fax : (44 131) 474 7031 email: [email protected] Internet: www.petex.com 1990-2011 Petroleum Experts Limited

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GAP

Table of Contents 0

Chapter 1

Technical Overview

2

1 Field Optimisation ................................................................................................................................... 4 2 Field Planning ................................................................................................................................... 5 3 Fluid modelling ................................................................................................................................... (PVT) 6 Introduction .......................................................................................................................................................... to Lumping/Delumping 6

4 Reservoir ................................................................................................................................... Modelling 10 5 Flow assurance ................................................................................................................................... and advanced thermal modelling options 11 6 Artificial ................................................................................................................................... Lift 12 7 Complex ................................................................................................................................... Well Geometry 13 8 Automation ................................................................................................................................... 14 9 The Core ................................................................................................................................... GAP Technique 15 About the.......................................................................................................................................................... Network Solver 15 About the.......................................................................................................................................................... Optimiser 16 Considerations .......................................................................................................................................................... on Optimisation 17

10 Examples ................................................................................................................................... Index 24 11 What's................................................................................................................................... New 26

Chapter 2

User Guide

38

1 What is ................................................................................................................................... in this guide? 38 2 Introduction ................................................................................................................................... 39 How to Use .......................................................................................................................................................... This Guide 41 GAP Glossary .......................................................................................................................................................... of Terms 42

3 Getting ................................................................................................................................... Started with GAP 44 The GAP.......................................................................................................................................................... User Interface 44 Opening ......................................................................................................................................................... a File 46 Saving ......................................................................................................................................................... a File 46 The System ......................................................................................................................................................... Window 47 The Toolbar ......................................................................................................................................................... 50 The Navigator ......................................................................................................................................................... Window 54 Drawing ......................................................................................................................................................... the System 56 The Preferences ......................................................................................................................................................... Dialog 59 Defining ......................................................................................................................................................... User Correlations 61 Edit Ini ......................................................................................................................................................... File 62 Defining ......................................................................................................................................................... the Working Directory 62 Printing ......................................................................................................................................................... from GAP 62 Exiting ......................................................................................................................................................... GAP 63 Project Archiving .......................................................................................................................................................... 64 Archive ......................................................................................................................................................... Creation 64 Archive ......................................................................................................................................................... Extraction 67 The Options .......................................................................................................................................................... Menu 70 Method ......................................................................................................................................................... 70 Edit Injection ......................................................................................................................................................... Fluids 76

Contents

II

Edit Tax ......................................................................................................................................................... Regimes 77 Edit Emulsion ......................................................................................................................................................... Models 78 Edit Default ......................................................................................................................................................... Settings 82 Edit System ......................................................................................................................................................... Summary 84 View......................................................................................................................................................... System Statistics 85 Disable ......................................................................................................................................................... Options 85 The View.......................................................................................................................................................... Menu 87 Draw......................................................................................................................................................... Options 88 Highlight ......................................................................................................................................................... Options 88 Highlight TVD ......................................................................................................................................... Differences 88 Highlight Violated ......................................................................................................................................... and Limiting Constraints 91 Window ......................................................................................................................................................... Aspect and Drawing Options 92 Select Info Displayed ......................................................................................................................................... 92 Select Default ......................................................................................................................................... Icon Label Position 92 Colours

......................................................................................................................................... 93

Icon Sizes ......................................................................................................................................... 94 Fonts

......................................................................................................................................... 94

Grid

......................................................................................................................................... 94

Network ......................................................................................................................................................... Drawing Position 95 Normalize Equipment ......................................................................................................................................... Icons Position and Snap to Grid 95 The Edit .......................................................................................................................................................... Menu 95 Undo......................................................................................................................................................... Options 96 Select ......................................................................................................................................................... Options 97 Selected ......................................................................................................................................................... Equipment Options 98 Selected Items ......................................................................................................................................... 99 Selected Wells ......................................................................................................................................... and Inflows 101 Selected Pipes ......................................................................................................................................... 102 Selected Tanks ......................................................................................................................................... 103 Selected Groups ......................................................................................................................................... 104 Find......................................................................................................................................................... Equipment on System Window 104 Edit......................................................................................................................................................... Options 106 Edit Equipment ......................................................................................................................................... Controls 106 Edit Project......................................................................................................................................... Paths 107 Transfer ......................................................................................................................................................... and Import Options 108 Transfer Well ......................................................................................................................................... Data from MBAL Models 108 Initialise IPRs ......................................................................................................................................... from Tank Simulations 110 Import Compositions ......................................................................................................................................... 111 Lump/Delump ......................................................................................................................................... Compositions 111 Transfer Options ......................................................................................................................................... for Gas Lift Injection 112 Execute ......................................................................................................................................................... OpenServer Statement 112 Importing ......................................................................................................................................................... GAP models in an existing project 113 The Constraints .......................................................................................................................................................... Menu 118 System ......................................................................................................................................................... Constraints 119 Binding ......................................................................................................................................................... (Yes/No) 121 Edit......................................................................................................................................................... Constraints Table 121 Edit......................................................................................................................................................... Abandonment Constraints Table 123

4 Describing ................................................................................................................................... the PVT 124 Black Oil .......................................................................................................................................................... 126 Compositional .......................................................................................................................................................... Options 128 EoS......................................................................................................................................................... Model Setup 129 More Lumping ......................................................................................................................................... 135 Setting ......................................................................................................................................................... up a Compositional model 139 Tracking ......................................................................................................................................................... 142 Fully ......................................................................................................................................................... Compositional 143

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Black ......................................................................................................................................................... Oil Compositional Lumping/Delumping 144 Viewing ......................................................................................................................................................... Compositional Results 145

5 Equipment ................................................................................................................................... Data 149 Introduction .......................................................................................................................................................... 149 Equipment .......................................................................................................................................................... Data Entry Screen Format 149 The......................................................................................................................................................... Navigator - Equipment list 150 Section ......................................................................................................................................................... Buttons 152 Summary ......................................................................................................................................... 152 Input Button ......................................................................................................................................... 152 Results Button ......................................................................................................................................... 153 Action ......................................................................................................................................................... Buttons 154 Wells .......................................................................................................................................................... 156 Well......................................................................................................................................................... Summary Screen 157 Calculate ......................................................................................................................................................... 161 Well......................................................................................................................................................... Input Screens 165 Tank Connections ......................................................................................................................................... 166 Multi-Layer................................................................................................................................... Case 167 IPR Input ......................................................................................................................................... 167 Ipr Layer input ................................................................................................................................... data 169 Composition ................................................................................................................................... 174 Action Buttons ................................................................................................................................... in IPR Input Screens. 174 More Layer................................................................................................................................... Data 177 Production................................................................................................................................... Data 180 Tight Gas ................................................................................................................................... IPR 182 Grid View ................................................................................................................................... 185 Abandonment ................................................................................................................................... Section 186 Note on water ................................................................................................................................... injector's IPR 188 VLP Input ......................................................................................................................................... 189 Inspection................................................................................................................................... of VLP Data 193 Well Constraints ......................................................................................................................................... 195 General Constraints ................................................................................................................................... 195 Gas Lifted................................................................................................................................... Wells Constraints 197 Diluent Injection ................................................................................................................................... Wells Constraints 197 ESP, HSP, ................................................................................................................................... PCP and Jet Pump Wells Constraints 198 Abandonment ................................................................................................................................... Constraints 200 Symbols ................................................................................................................................... 201 Notes on Constraints ................................................................................................................................... 201 Controls

......................................................................................................................................... 202

Symbols ................................................................................................................................... 202 dP Control................................................................................................................................... 203 Gas Lift Control ................................................................................................................................... 204 ESP Control ................................................................................................................................... 205 Diluent Control ................................................................................................................................... 206 HSP Control ................................................................................................................................... 207 Jet Pump Control ................................................................................................................................... 208 PCP Control ................................................................................................................................... 209 Fluids Property ................................................................................................................................... Setup 209 PC Data ......................................................................................................................................... 210 PC Generation ................................................................................................................................... 211 Downtime ......................................................................................................................................... 212 Coning (For......................................................................................................................................... Oil Producers Only) 212 Schedule (ONLY ......................................................................................................................................... for Prediction) 214 Outflow ......................................................................................................................................................... Only Well 216 Outflow Only ......................................................................................................................................... - VLP 218

Contents

IV

Outflow Only ......................................................................................................................................... - PROSPER 219 Importing the ................................................................................................................................... equipment data from PROSPER 220 Entering The ................................................................................................................................... Equipment in GAP Directly 225 Completing................................................................................................................................... the Outflow Only Well - Inflow Performance Setup 225 Well......................................................................................................................................................... Results Screen 226 Gradient Results ......................................................................................................................................... 227 Well Layer......................................................................................................................................... Results 228 Reporting Results ......................................................................................................................................... 229 Separators .......................................................................................................................................................... (Production / Injection) 230 Separator ......................................................................................................................................................... Summary Screen 232 Separator ......................................................................................................................................................... Input Screens 234 Separator Constraints ......................................................................................................................................... 234 Separation......................................................................................................................................... (PRODUCTION Separators ONLY) 237 Injection ......................................................................................................................................................... Fluid Details (INJECTION Man.Only) 237 Schedule (PREDICTION ......................................................................................................................................... Cases ONLY) 239 Steam Stream ......................................................................................................................................... 240 Oil Injection......................................................................................................................................... manifold 246 Joints .......................................................................................................................................................... 247 Joint ......................................................................................................................................................... Summary Screen 247 Joint ......................................................................................................................................................... Input Screen 248 Joint ......................................................................................................................................................... Constraints 249 Schedule ......................................................................................................................................................... 250 Pipelines .......................................................................................................................................................... 251 Pipeline ......................................................................................................................................................... Summary Screen 252 GAP ......................................................................................................................................................... Internal Correlations 254 Pipe Input Data ......................................................................................................................................... 255 Pipe Environment ................................................................................................................................... 255 Pipe Description ................................................................................................................................... 256 Pipe Entry................................................................................................................................... Example 262 Pipeline Pressure ................................................................................................................................... Matching 265 Entering Pipe ................................................................................................................................... Match Data 265 The Match................................................................................................................................... Calculation 266 Constraints ................................................................................................................................... 269 Schedule (ONLY ................................................................................................................................... for Prediction) 269 Pressure/Temperature ......................................................................................................................................... gradient result 271 Using ......................................................................................................................................................... Lift Curves for the Pipeline Pressure Drops 274 External

......................................................................................................................................... 275

GAP Internal ......................................................................................................................................... Correlations 276 PROSPER......................................................................................................................................... on line 280 PROSPER......................................................................................................................................... file 282 PROSPER ......................................................................................................................................................... On Line Pressure Drops 283 Edit Pipe entry ......................................................................................................................................... 284 Rough Approximation ................................................................................................................................... 286 Enthalpy Balance ................................................................................................................................... 287 Improved Approximation ................................................................................................................................... 293 Gradient ......................................................................................................................................................... Calculation 295 Bottlenecks ......................................................................................................................................................... 298 Emulsion ......................................................................................................................................................... correction 299 Wax ......................................................................................................................................................... or Hydrate Risk 303 Tanks .......................................................................................................................................................... 304 Tank ......................................................................................................................................................... Summary Screen 306 Tank ......................................................................................................................................................... Input Data (Material Balance Tank) 308 Constraints......................................................................................................................................... 308 Wells

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Injection

......................................................................................................................................... 310

Tank Schedule ......................................................................................................................................... 311 Tank Results ......................................................................................................................................... 311 Tank ......................................................................................................................................................... Input Data (Decline Curve Tank) 311 Tank Production ......................................................................................................................................... Data 312 Compressibility ......................................................................................................................................... 313 Flares and .......................................................................................................................................................... Vents 314 Summary ......................................................................................................................................................... and Input 314 Results ......................................................................................................................................................... 314 Pumps .......................................................................................................................................................... 315 Pump ......................................................................................................................................................... Summary Data 316 Pump ......................................................................................................................................................... Input Data 318 Jet ......................................................................................................................................................... Pumps Option 320 Pump ......................................................................................................................................................... Calculate Button 322 Pump ......................................................................................................................................................... Control 324 Pump ......................................................................................................................................................... Schedule (ONLY for prediction) 325 Compressors .......................................................................................................................................................... 326 Compressor ......................................................................................................................................................... Summary Data 326 Input ......................................................................................................................................................... Data for Compressor (Full Model) 327 Input ......................................................................................................................................................... Data for Fixed dP Compressor 334 Input ......................................................................................................................................................... Data for Fixed Power Compressor 335 Input ......................................................................................................................................................... Data for Reciprocating Compressor 337 Compressor ......................................................................................................................................................... Control (Full Model Only) 338 Compressor ......................................................................................................................................................... Schedule (ONLY for Prediction) 338 Compressor ......................................................................................................................................................... Calculate Button 339 Operating ......................................................................................................................................................... point in Plot 339 Surge ......................................................................................................................................................... and Choke 340 Efficiency ......................................................................................................................................................... vs rate 340 Sources.......................................................................................................................................................... / Sink 341 Source ......................................................................................................................................................... 341 Source Data ......................................................................................................................................... Entry 343 Source Summary ................................................................................................................................... Data 343 Source Data ................................................................................................................................... Input 345 Source Schedule ................................................................................................................................... (ONLY for Prediction) 346 Steam Stream ................................................................................................................................... 346 Sink......................................................................................................................................................... 346 Sink Data Entry ......................................................................................................................................... 347 Sink Summary ......................................................................................................................................... Data 347 Sink Input Data ......................................................................................................................................... 348 Sink Schedule ................................................................................................................................... (ONLY for Prediction) 348 Inline Elements .......................................................................................................................................................... 348 Inline ......................................................................................................................................................... Gate Valve 349 Inline gate ......................................................................................................................................... Valve Data Summary Screen 350 Input Data ......................................................................................................................................... / Schedule ( ONLY for prediction) 350 Inline ......................................................................................................................................................... Check Valve 351 Inline Check ......................................................................................................................................... Valve Data Summary Screen 351 Input Data ......................................................................................................................................... / Schedule ( ONLY for prediction) 352 Inline ......................................................................................................................................................... Separation 352 Inline Separation ......................................................................................................................................... Data Summary Screen 352 Inline Separation ......................................................................................................................................... Data Input Screen 353 Input Data ......................................................................................................................................... / Schedule (ONLY for prediction) 353 Inline ......................................................................................................................................................... Choke 353 Inline Choke ......................................................................................................................................... Data Summary Screen 354 Inline Choke ......................................................................................................................................... dP Control 355

Contents

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Input Data ......................................................................................................................................... / Schedule (ONLY for prediction) 357 Inline ......................................................................................................................................................... Injection 357 Inline Injection ......................................................................................................................................... Data Summary Screen 357 Inline Injection ......................................................................................................................................... Data Input Screen 358 Defining the ................................................................................................................................... Injection Rate 358 Defining the ................................................................................................................................... Injection Fluid PVT 360 Schedule (ONLY ......................................................................................................................................... for prediction) 360 Inline ......................................................................................................................................................... General 360 Notes on Inline ......................................................................................................................................... General Elements 361 Inline General ......................................................................................................................................... Input Data (Script) Screen 362 Inline General ......................................................................................................................................... Script Variables 362 Schedule (ONLY ......................................................................................................................................... for prediction) 363 Inline Element ......................................................................................................................................... Variables 363 Control Variables ......................................................................................................................................... 365 Temporary ......................................................................................................................................... Variables 366 Results Variables ......................................................................................................................................... 366 Tax Regime ......................................................................................................................................... Variables 367 FLOW and......................................................................................................................................... COMP Structure Variables 367 PVT Calculator ......................................................................................................................................... - Black Oil 370 PVT Calculator ......................................................................................................................................... - Compositional 372 Logging Messages ......................................................................................................................................... 374 Mathematical ......................................................................................................................................... Functions 375 Control Structures ......................................................................................................................................... 376 Example Script ......................................................................................................................................... 377 Inflow Icon .......................................................................................................................................................... 378 Inflow ......................................................................................................................................................... Summary Screen 378 Input ......................................................................................................................................................... 379 Grouping .......................................................................................................................................................... 379 Grouping ......................................................................................................................................................... Data Entry 380 Constraints......................................................................................................................................... 380 Schedule ......................................................................................................................................... 381 Grouping ......................................................................................................................................... 382 Flowsheets .......................................................................................................................................................... 384 Summary, ......................................................................................................................................................... Input, Results 388 Notes on .......................................................................................................................................................... Constraints 388

6 VLP/IPR ................................................................................................................................... Generation 388 A well model .......................................................................................................................................................... in GAP 389 IPR......................................................................................................................................................... 390 VLP......................................................................................................................................................... 390 Importance ......................................................................................................................................................... of VLP Data Ranges 390 Batch Generation .......................................................................................................................................................... of IPR’s 390 Single ......................................................................................................................................................... layer wells 390 Multilayer ......................................................................................................................................................... wells 394 Batch Generation .......................................................................................................................................................... of Well and Pipe VLPs 402 Batch ......................................................................................................................................................... Generation of VLPs 402 Values ......................................................................................................................................................... to use for VLP Generation 408 Generating ......................................................................................................................................................... Well VLP on a well-by-well basis 412 Batch ......................................................................................................................................................... Generation of VLPs with Mass flow rates 414 Batch ......................................................................................................................................................... Generation of Pipe VLPs 418 Batch Generation .......................................................................................................................................................... of Well Performance Curves 420

7 Model................................................................................................................................... Validation 425 Well Model .......................................................................................................................................................... Validation 425 Checking .......................................................................................................................................................... Wells Calibration 425

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Running ......................................................................................................................................................... Model Validation / Quality Check 426 Checking ......................................................................................................................................................... the Quality of Individual Wells Graphically 430

8 Network ................................................................................................................................... Solver and Optimiser 434 The Solver .......................................................................................................................................................... 434 The Optimiser .......................................................................................................................................................... 434 Constraints .......................................................................................................................................................... and Equipment Control Screen 434 Constraints ......................................................................................................................................................... 434 Equipment ......................................................................................................................................................... Control Screen 435 Optimisation ......................................................................................................................................................... Objective Function 437 Solving.......................................................................................................................................................... the Network 440 Solver Modes .......................................................................................................................................................... 441 No Optimisation ......................................................................................................................................................... 442 Optimise ......................................................................................................................................................... with all constraints 443 Optimise ......................................................................................................................................................... with potential constraints only 444 The Solver .......................................................................................................................................................... / Optimiser Settings 444 Calculation .......................................................................................................................................................... Results 451

9 Prediction ................................................................................................................................... 453 Prediction .......................................................................................................................................................... - Basics 455 Forecast ......................................................................................................................................................... Workflow 455 Linking ......................................................................................................................................................... MBAL files to GAP 456 Prediction ......................................................................................................................................................... Execution and Results 457 Notes ......................................................................................................................................................... on Constraints 463 Linking ......................................................................................................................................................... Production / Injection Forecasting 464 Prediction .......................................................................................................................................................... Options 467 Run......................................................................................................................................................... Prediction 468 View ......................................................................................................................................................... Prediction Log 468 Save ......................................................................................................................................................... Prediction Results as 469 Reload ......................................................................................................................................................... Prediction Snapshot 472 Prediction ......................................................................................................................................................... Script Options 473 Edit......................................................................................................................................................... System Constraints Schedule 474 Notes on Constraints ......................................................................................................................................... 475 Edit......................................................................................................................................................... Separator and Joint Schedules 476 Edit......................................................................................................................................................... Equipment Schedule 479 Edit......................................................................................................................................................... Tank Schedule 482 Edit......................................................................................................................................................... Gas lift Schedule 484 Edit......................................................................................................................................................... DCQ Schedule 486 Edit......................................................................................................................................................... Schedule Event Groups 487 Apply ......................................................................................................................................................... Schedule to 489 Purge ......................................................................................................................................................... Results 490 Plot......................................................................................................................................................... and View the Prediction Results 490 Plot Nodes......................................................................................................................................... Prediction Results 491 Plot Tanks ......................................................................................................................................... Prediction Results 493 Plot Emissions ......................................................................................................................................... Prediction Results 493 View DCQ ......................................................................................................................................... Prediction Results 493

10 Results ................................................................................................................................... and Reports 494 Results .......................................................................................................................................................... Menu 495 Detailed ......................................................................................................................................................... Results 495 Summary ......................................................................................................................................................... Results 496 Total ......................................................................................................................................................... System Results 498 System ......................................................................................................................................................... Emissions 499 Plot......................................................................................................................................................... Performance Curves... 501 Plot......................................................................................................................................................... Options 502 Reports.......................................................................................................................................................... 508

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11 History ................................................................................................................................... Matching an IPM Model 510 Introduction .......................................................................................................................................................... 511 Procedure .......................................................................................................................................................... for History Matching 511 Running ......................................................................................................................................................... the model and comparing to history 512 History ......................................................................................................................................................... matching each element independently 512

12 Prediction ................................................................................................................................... Script 520 Introduction .......................................................................................................................................................... 520 Functions .......................................................................................................................................................... 521 Example .......................................................................................................................................................... 522

13 Defining ................................................................................................................................... System Units 525 Defining.......................................................................................................................................................... the Global Unit System 525 Setting .......................................................................................................................................................... the Input / Output Unit System 526 The Control .......................................................................................................................................................... Database 527 Defining.......................................................................................................................................................... Units at a Variable Level (Dynamic Unit Conversions) 528

Chapter 3

Examples Guide

531

1 Examples ................................................................................................................................... Index 531 Extracting .......................................................................................................................................................... a GAP Archive file (.GAR) 533

2 Example ................................................................................................................................... 1 - Gas Field Network modelling with GAP 535 Objectives .......................................................................................................................................................... 535 Data available .......................................................................................................................................................... 536 Build the .......................................................................................................................................................... GAP model 537 Draw ......................................................................................................................................................... the GAP Network 537 Define ......................................................................................................................................................... the Reservoir 545 Define ......................................................................................................................................................... the Wells 547 Generate ......................................................................................................................................................... Well IPRs 549 Generate ......................................................................................................................................................... Well VLPs 552 Define ......................................................................................................................................................... the Pipelines 554 Setting ......................................................................................................................................................... Schedules, Constraints and Well Controls 564 Running.......................................................................................................................................................... the Prediction 567 Results ......................................................................................................................................................... 570

3 Example ................................................................................................................................... 2 - Oil Production Network 574 Objectives .......................................................................................................................................................... 574 Data available .......................................................................................................................................................... 575 Build the .......................................................................................................................................................... GAP model 577 Draw ......................................................................................................................................................... the GAP Network 577 Define ......................................................................................................................................................... the Reservoirs 583 Define ......................................................................................................................................................... the Wells 584 Generate ......................................................................................................................................................... Well IPRs 585 Generate ......................................................................................................................................................... Well VLPs 587 Model ......................................................................................................................................................... Validation to QC the wells 589 Define ......................................................................................................................................................... the Pipelines 590 Question .......................................................................................................................................................... 1 - Solution 596 Initialise ......................................................................................................................................................... IPRs from Tank Simulations 596 Solve ......................................................................................................................................................... network for wells fully open 598 Question .......................................................................................................................................................... 2 - Solution 601 Entering ......................................................................................................................................................... the Constraint 601 Setting ......................................................................................................................................................... Well Controls 601 Solve ......................................................................................................................................................... Network with Optimisation 602 Question .......................................................................................................................................................... 3 - Solution 605 Run......................................................................................................................................................... Prediction with Optimisation 605 Saving ......................................................................................................................................................... the Prediction results 609

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Question .......................................................................................................................................................... 4 - Solution 610 Setting ......................................................................................................................................................... a Schedule 610 Run......................................................................................................................................................... Prediction with Optimisation 611 Comparing......................................................................................................................................... scenarios 615

4 Example ................................................................................................................................... 3 - Pipeline detailed results 619 Objectives .......................................................................................................................................................... 619 Data available .......................................................................................................................................................... 619 Run Solve .......................................................................................................................................................... Network 619 Pipeline.......................................................................................................................................................... detailed results 621 Note on.......................................................................................................................................................... pipeline results 624 Convert ......................................................................................................................................................... the pipeline to PROSPER on line 625

5 Example ................................................................................................................................... 4 - Gas Lift Optimisation 628 Objectives .......................................................................................................................................................... 628 Data Available .......................................................................................................................................................... 629 Build the .......................................................................................................................................................... GAP Network 630 Draw ......................................................................................................................................................... the GAP Network 631 Define ......................................................................................................................................................... the wells 636 Generate ......................................................................................................................................................... Well IPRs 639 Generate ......................................................................................................................................................... Well VLPs 641 Define ......................................................................................................................................................... the Pipelines 643 Scenario .......................................................................................................................................................... with fixed allocation 646 Enter ......................................................................................................................................................... current gas lift allocation 647 Solve ......................................................................................................................................................... Network with No Optimisation 649 Solve Network .......................................................................................................................................................... with optimised gas lift allocation 651 Set......................................................................................................................................................... gas lift Controls 651 Solve ......................................................................................................................................................... Network with Optimisation 651

6 Example ................................................................................................................................... 5 - Gas Lift Injection Network 654 Objectives .......................................................................................................................................................... 654 Data Available .......................................................................................................................................................... 655 Modify the .......................................................................................................................................................... production network 656 Generate ......................................................................................................................................................... the well VLPs in PROSPER 657 Setting ......................................................................................................................................................... well Controls in GAP 660 Build the .......................................................................................................................................................... Gas Lift Injection Network 662 Draw ......................................................................................................................................................... the GAP Network 662 Define ......................................................................................................................................................... the Wellheads 668 Define ......................................................................................................................................................... Pipelines and surface equipment 669 Link the.......................................................................................................................................................... production to the gas injection network 671 Solve Network .......................................................................................................................................................... with Optimisation including Gas Lift Injection Network 673

7 Example ................................................................................................................................... 6 - Electric Submersible Pump - Model Calibration 678 Objectives .......................................................................................................................................................... 678 Data Available .......................................................................................................................................................... 679 Build the .......................................................................................................................................................... GAP model 680 Draw ......................................................................................................................................................... the GAP Network 680 Define ......................................................................................................................................................... the Wells 686 Generate ......................................................................................................................................................... Well IPRs 688 Import ......................................................................................................................................................... Well VLPs 690 Model ......................................................................................................................................................... validation to QC wells 691 Define ......................................................................................................................................................... the Pipelines 694 Present.......................................................................................................................................................... production 698 Well......................................................................................................................................................... Controls 698 Solve ......................................................................................................................................................... Network without Optimisation 699 Optimising .......................................................................................................................................................... production 702 Constraint ......................................................................................................................................................... on maximum power 702

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Well......................................................................................................................................................... Controls 703 Solve ......................................................................................................................................................... Network with Optimisation 705

8 Example ................................................................................................................................... 7 - Associated Water Injection System 709 Objectives .......................................................................................................................................................... 709 Data available .......................................................................................................................................................... 710 Prediction .......................................................................................................................................................... to determine water injection requirement 710 Determine .......................................................................................................................................................... number fo injection wells 713 Associate .......................................................................................................................................................... production to water injection model 716 Run Prediction .......................................................................................................................................................... with coupled models 718

9 Example ................................................................................................................................... 8 - Prosper On-line Pipeline 724 Objectives .......................................................................................................................................................... 724 Data Available .......................................................................................................................................................... 725 Convert.......................................................................................................................................................... the pipe to PROSPER on line 725 Run calculation .......................................................................................................................................................... and read results 728 Importing .......................................................................................................................................................... an existing PROSPER model 734

10 Example ................................................................................................................................... 9 - Programmable inline element 737 Objectives .......................................................................................................................................................... 737 Data available .......................................................................................................................................................... 738 Define the .......................................................................................................................................................... Inline Programmable 738 Run calculation .......................................................................................................................................................... and view results 741

11 Example ................................................................................................................................... 10 - Smart Well Modelling in GAP 743 Objectives .......................................................................................................................................................... 743 Data Available .......................................................................................................................................................... 744 Build the .......................................................................................................................................................... GAP Network 744 Draw ......................................................................................................................................................... the GAP Network 746 Define ......................................................................................................................................................... the IPR elements 749 Define ......................................................................................................................................................... the Pipe CD 752 Define ......................................................................................................................................................... the Outflow AB 753 Making ......................................................................................................................................................... the gas inflow controllable 755 Solve Network .......................................................................................................................................................... with no Optimisation 756 Solve Network .......................................................................................................................................................... with Optimisation 758

12 Example ................................................................................................................................... 11 - GAP Fully Compositional 761 Objectives .......................................................................................................................................................... 761 Data Available .......................................................................................................................................................... 763 Build the .......................................................................................................................................................... GAP model 764 Draw ......................................................................................................................................................... the GAP network 764 Define ......................................................................................................................................................... the Reservoir 767 Setting ......................................................................................................................................................... up MBAL as compositional 768 Entering compositional ......................................................................................................................................... PVT Data 770 Define ......................................................................................................................................................... the Wells 775 Generate ......................................................................................................................................................... Well IPRs 777 Import ......................................................................................................................................................... VLPs 777 Import ......................................................................................................................................................... EoS Composition in GAP 778 Define ......................................................................................................................................................... the Pipelines 781 Completing ......................................................................................................................................................... the model 782 Solve Network .......................................................................................................................................................... and viewing results 783 Viewing ......................................................................................................................................................... the detailed compositional results 786 Prediction .......................................................................................................................................................... and viewing results 790

13 Example ................................................................................................................................... 12 - Compositional Lumping/Delumping 795 Objectives .......................................................................................................................................................... 795 Data Available .......................................................................................................................................................... 796 Create and .......................................................................................................................................................... export the Lumped and the De-lumped compositions 796

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Enter ......................................................................................................................................................... the lumped/de-lumped composition in MBAL 802 Enter ......................................................................................................................................................... the lumped/de-lumped composition in GAP 806 Prediction .......................................................................................................................................................... and viewing the results 811

14 Example ................................................................................................................................... 13 - Black Oil Compositional Lumping-Delumping 816 Objectives .......................................................................................................................................................... 816 Data Available .......................................................................................................................................................... 817 Set up GAP .......................................................................................................................................................... as Black Oil compositional Lumping/Delumping 817 Solve Network .......................................................................................................................................................... and results 820 Prediction .......................................................................................................................................................... and viewing the results 822 Black Oil .......................................................................................................................................................... - Lumping/Delumping 825

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1 Technical Overview PETROLEUM EXPERTS GAP (General Allocation Package) is a multiphase flow simulator that is able to model and optimise production and injection networks. The concept of network is here intended as general, therefore both surface and downhole. GAP is part of the IPM Suite, and allows the engineer to build complete system models, including the reservoirs, wells and surface network. GAP can be linked directly to PROSPER and MBAL to model entire reservoir and productions systems and to reservoir numerical simulators (REVEAL, Eclipse, Imex, GEM, etc.), process simulators (Hysys, Unisim) and spreadsheets through Petroleum Experts controller RESOLVE . GAP can model production and injection systems where any type of fluid can be present: oil, dry and wet gas, gas retrograde condensate, steam and user-defined, in addition to gas or water injection systems. The fluid phase behaviour can be modelled using black oil formulation or Equation of State compositional modelling. The rigorous compositional modelling capabilities of GAP enable to perform studies where the determination of the fluid composition is crucial (for example, for environmental restrictions or in order to satisfy the requirements at process level), or necessary to determine the conditions at which there is precipitation of solids for Flow Assurance (wax and hydrate deposition). Calculation can be performed for the status of the system at a specific point in time (Solve Network) or along the time (Prediction), making us of the connected reservoir simulator ( MBAL or any numerical simulator) to model the reservoir depletion. GAP allows to model and optimise surface and downhole networks. Its powerful calculation engines allow to model and optimise very complex networks, composed by thousands of elements: wells, pipelines, compressors, pumps, heat exchangers, etc, connected in any possible way (i.e. complex loops). GAP has the most powerful and fastest optimisation engine in the industry, as it is based on non-linear SQP technique 17 (Sequential Quadratic Programming). The GAP optimiser allows to optimise the system, which means: - To Maximise a certain objective function (for example: oil production or both oil and gas production) - and, at the same time, to Honour any constraint set in the system The GAP optimiser allows to determine how wellhead chokes need to be set, compressors and pumps operated, and gas allocated for gas lifted wells, to maximise Production or Revenue while honouring constraints at any level.

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GAP is characterised by a fully open architecture (OPENSERVER), which enables the user to access all the features of the software from a third party application (Excel macros, Visual Basic, C, etc.). OPENSERVER allows to automatise tasks like updating the models, running sensitivities and also to enhance greatly the capabilities of the model itself by allowing the implementation of complex workflows executed using the model.

MAIN APPLICATIONS The fields of applications of GAP can be divided in the following groups: Field Optimisation Field Planning

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Reservoir modelling 10 Flow assurance and advanced thermal modelling options 11 Artificial lift

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Complex well geometry 13 Automation 14 Examples Index 24

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1.1 Field Optimisation GAP features the fastest and most efficient optimiser in the industry, based at its core on the non-linear SQP 17 technique. The Optimisation feature allows the user to determine the best settings to apply in the field (wellhead chokes, inline chokes, gas lift allocation, etc.) in order to maximise a certain objective function (for example, oil production) and at the same time honour constraints entered in the system. Some applications of the Optimisation feature are: Full field Optimisation studies with mixed systems (ESP, GL, Naturally Flowing) Field management Field Gas Lift Optimisation Advises on wellhead chokes settings to meet reservoir management targets Multi-phase Looped Network Optimisation GAP links to PROSPER (well model) and MBAL (tank model) to allow entire production systems to be modelled and optimised over the life of the field Injection system optimisation - studies of pressure support Back to Overview

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1.2 Field Planning The unique forecasting and optimisation capabilities of GAP allow top achieve several objectives in the scope of Field Planning: Production forecasts using reservoir models (MBAL directly in GAP or numerical simulators through RESOLVE) Full field forecasting optimisation Field Management Day to day field operation optimisation Optimisation of injection strategies - pressure support studies Back to Overview

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1.3 Fluid modelling (PVT) Modelling accurately the fluid behaviour has become more and more important as the Integrated Production Modeling approach has been extended to more disciplines (see below 6 ). In GAP various options are available to accurately model the fluid PVT properties, depending on the objectives and the available data: Black oil Black oil model is used for the calculation. Tracking This method is based on a combination of black oil model and full compositional model (equation of state or EOS): - Black oil model is used for the main pressure drop calculations - The EOS is then used as a post calculation to determine the composition in any part of the system by performing compositional blends and flashes whenever necessary. If a black oil reservoir simulator (like for example MBAL), the compositional tracking provides with the unique capability to recombine the initial composition in order to match the GOR of the fluid produced. Fully Compositional This method allows to run all the calculations using an equation of state, which gives the compositions as well as the fluid PVT properties in any point of the network. NEW!!! This option allows also to perform Lumping/Delumping of an initial EOS, which empowers the user with the possibility to decide if running the calculations using an extended composition, or a using a composition with a reduced number of components (lumped). Black Oil Compositional Lumping/Delumping NEW!!! To speed-up calculations, the Black Oil Lumping/Delumping method tracks the composition of the fluids throughout the network at each iteration of the solver, but performs pipeline, compressor, pump, choke, ... calculations using the Black Oil PVT correlations based on the black oil standard condition properties calculated by the equation of state. Black Oil Lumping/Delumping may use the full or the lumped compositions. Back to Overview

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1.3.1 Introduction to Lumping/Delumping Today the technology available (IPM RESOLVE) allows to integrate and optimise reservoir simulation models (REVEAL, Eclipse and other third party simulators, etc.) to production and injection network models (GAP) up to process models (Hysys, Unisim). With regards to the PVT modelling, each application has got its own requirements, which are GAP User Guide

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dictated on one side by the objectives of the application itself and on the other by the calculation speed. The figure below summarises the main requirements for the three main classes of simulators:

Reservoir numerical simulators are generally focused more on volumetric properties and the phase behaviour. PVT modelling can be carried out by means of black oil or compositional (EOS). In case of EOS modelling, the number of components has to be limited to a very few to avoid the model to run too slow (with exception of thermal simulators like REVEAL, where a larger number of components is required to guarantee accurate thermal calculations) Surface network simulators can work in black oil or compositional too and are focused mainly on densities and viscosities, as these affect mostly the pressure losses. As far as the EOS is concerned, the number of components has to be decided on the basis of the model objectives: if it only to determine the pressure drops, a small number of components can be suitable and can reduce the run time. However, if the objective is to perform detailed flow assurance studies (temperature estimations, hydrates, etc.), an extended composition will be necessary. Process simulators, on their side, focus more on thermal properties calculations, therefore they require compositional modelling and the composition needs to have a large number of components. This is because the thermal properties can be accurately estimated only by specifying in detail the composition. Density is by default determined on the basis of a correlation (Costald) In general, when connecting different model together, the common factor among them is the fluid. In other words, it is necessary to be able to use a PVT characterisation that is consistently valid throughout the system. Based on the information above, whenever a composition is required - because a process simulator is connected, or because detailed studies need to be performed - it is required to be able to pass from a small number of components to a large one (or viceversa) whenever desired/necessary, and to make sure that the fluid characterisation is representative of the actual fluid throughout.

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The idea behind compositional Lumping/De-lumping is to have a methodology that is able to pass from an extended composition (de-lumped or "full" in the following) to a reduced one (lumped or grouped) and vice-versa consistently, that is to say, preserving the quality of the characterisation. This means that at any point in time the full and the lumped compositions will be equivalent and representative of the real fluid. In general when creating two characterisations of the same fluid, by definition they will not give the same answers. However, lumping/de-lumping has to make sure that the important properties are consistent, so that calculation speed and accuracy are both satisfactory.

In GAP this is achieved by means of the so-called "Lumping Rule", which is a piece of logic that defines the mechanisms to pass from the full to the lumped composition. The Lumping Rule is created at the stage of building the EOS model using Petroleum Experts' PVT package PVTP. PVTP has all the facilities to create and quality check the couple full/lumped compositions and to create the Lumping Rule. An example of a possible Lumping Rule is reported below:

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In GAP it is possible to import a Lumping Rule, which is then used to generate the lumped (or the full) composition when desired, and (if required) the pair full / lumped compositions. It is then possible to decide if to run the calculations with the full or with the lumped composition. The following example illustrates one of the possible applications: Extended composition is required because thermal studies on the pipelines need to be carried out Reservoir simulator - PVT is defined with EOS with 5 components (lumped) Surface network model (GAP) - full composition is required because detailed thermal properties are required In this case GAP will run using the full composition, which is determined on the basis of the lumped composition coming from the simulator.

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1.4 Reservoir Modelling GAP allows to model and optimise the whole production and injection system by integrating reservoir models to well models to the model of the pipeline/surface gathering network. The reservoir can be modelled by importing directly in GAP material balance models (MBAL) or by linking GAP to the reservoir simulator using IPM controller RESOLVE. Back to Overview

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1.5 Flow assurance and advanced thermal modelling options GAP allows to accurately model at the same time well and pipeline hydraulics and surface facilities (compressors, pumps, etc. The pipeline network can be characterised by very complex topology (with hundreds or thousands of elements and pipe loops). This allows to perform studies for: Full field surface network design Flow assurance: detailed pipeline studies 271 , temperature modelling, erosion onset, hydrate formation, waxes deposition, condensed water vapour, etc. Process facilities design (for example, design of slug catchers and separators) Artificial lift optimisation and operation Compressor and Pump system design Use the "Improved Approximation" temperature model for improved temperature calculations. Note: The temperature model "improved approximation" is to be selected in the system options screen under |Options | Method. Once the improved approximation is selected, the user can enter a pipe depth dependent Uvalue. In the event the pipe-depth dependent U-value is missing, GAP uses the U-value entered on the pipe environment description screen. Features: PROSPER on line for advanced temperature modelling (Enthalpy Balance, Improved Approximation) Improved approximation available with GAP Internal Correlations pressure drop model Programmable elements allowing modelling of even complex equipment Back to Overview

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1.6 Artificial Lift In GAP modelling and artificial lift optimisation can be carried out: Gas lift (Continuous) Electrical Submersible Pump (ESP) Hydraulic Submersible Pump (HSP) Jet Pump Progressive Cavity Pump (PCP) Diluent Injection Features: Full field Optimisation studies where naturally flowing, gas lift and ESP wells can all be included in the same production system model Modelling of Gas Lift Network along with production network (NEW!!!) Detailed reporting of pump results (head, power consumption, etc.) Back to Overview

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1.7 Complex Well Geometry GAP has a number of modelling facilities that are able to replicate accurately even very complex well geometries (smart wells, multilateral wells, wells with Inflow controllable devices) and even to optimise them. One typical example is horizontal completions with ICVs, where one wants to understand how to set the downhole valves in order to maximise production on one side and prevent gas coning on the other. Main features: Well inflow and outflow elements to decompose the wellbore Pipeline elements can have tubing or annular flow patterns PROSPER on line allowing the use of rigorous temperature models Back to Overview

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1.8 Automation GAP features OPENSERVER, which allows to access all of the capabilities of GAP from a external applications: macros, VB, C, etc. This allows the user to automatise many of the tasks that can be performed by operating the program GUI and to code His/Her own workflows. Along the years this feature has been applied to achieve a vast variety of objectives. These are only a few examples of those applications: Model validation and update Interfaced to data sources to run scenarios Field management Well routing policies Field planning Building interfaces to the GAP model to run customised calculations (deployed directly on the field) Interfacing GAP to specialised tools to perform special studies (for example, corrosion studies) Back to Overview

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1.9 The Core GAP Technique Production and Injections systems include producing / injecting elements (wells) that are connected via common manifolds and pipelines to a fixed system pressure called separator in GAP. The separator in GAP does not have to be the physical separator in the field; it is simply a point of fixed pressure in the network. Nodes are connections or calculation points. The core GAP technique has 2 levels: Level 1: Solving the network Level 2: Optimising the network response

1.9.1 About the Network Solver In the figure below, the fluid contribution can be from wells or sources:

For each node, one can write:

C = Constant

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There are as many equations as unknowns. This set of equations is solved numerically. It is the “natural” response of the network.

1.9.2 About the Optimiser The solution that is generated by the solver i.e. the “natural" response of the system may not be the optimum. The network may be capable of higher production rates, by altering certain conditions, like: Back pressure of wells by applying wellhead chokes. Gas-lift gas allocated to individual gas lifted wells. Frequency of operation of ESP fitted wells Frequency of operation of pumps / compressors. Inline choke sizes The optimiser of GAP can do this task. Apart from boundary conditions i.e. fixed pressure values (separator pressures) in the system the optimiser can also honour various constraints such as: Maximum oil / gas production System constraints (min water production, max pressure constraint, velocity constraints, etc.). The optimiser will achieve the maximum hydrocarbon production using the rate of change of the production rate with respect to the rate of change controllable variables, e.g. of the injected lift gas rate for gas lifted wells. GAP handles naturally flowing, gas lifted and ESP equipped producing wells in addition to water and gas injectors. Optimisation can be based on Gross revenue Maximum oil production There is no upper limit on the number of wells and/or platforms that can be entered. Constraints can be considered at all levels e.g. well, joint, separator and total system. Production Forecast models can also consider constraints at the reservoir tank level. The key element of this method is the quality of the well models.

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1.9.3 Considerations on Optimisation There are several methods for optimisation available in the literature, some of them simple (like Simplex (Linear Programming) and Equal Slope), others much more complex, like SQP (Sequential Quadratic Programming). This section will provide a brief conceptual description of these methods and explain why GAP uses SQP, which is the most difficult and sophisticated optimisation technique to implement. This explanation will concentrate on a Gas Lifted system as it is the best system to explain the non-linearity of a field and how it can be addressed from an optimisation point of view. Consider the following very simple function:

This has a clear maximum in the X region we are looking into, indicated by the red arrow on the plot above. In a linear system, two methods can be applied to determine the maximum of this function: Bracketing Derivatives The first Method is based upon trying different guesses of X and calculating Y. After trying a number of X guesses, the maximum is “Bracketed” and reached. The following diagram shows the approach:

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The derivatives approach works on the basis of Gradients: The derivative of Y is calculated with respect to X and then set to 0. This will allow calculation of all (X,Y) points which are maxima, minima or points of inflection. The second derivative of the function can then be used to determine the nature of each calculated point and the maximum determined. Both of these methods work very well for linear problems where Y can be described as a direct function of X. In the context of a field, this is the case of a dry gas field with no water production in which pressure at every point is a direct function of the flowrate. A non linear system will not behave in the same way. By the very nature of it, each time a guess of X is taken in order to calculate the corresponding Y, the Y function itself changes as it may be dependent on other variables affected by the choice of X. The following diagram will show how the function will behave for a choice of X:

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This, in effect, represents a moving target and trying to determine the optimum with Linear Programming techniques will not succeed. Consider now the case of a Gas Lift Injection network (shown in a simplified diagram below):

This is made up of two gas lifted wells and the objective is to determine what is the optimum gas lift injection rate to inject in each in order to achieve maximum production from the system. Linear Programming techniques will work based on the response of the well. The Performance curve of the well on the right (with one fixed WHP) will be:

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In the quest for the Optimum Gas Lift Injection Rate, a guess for Injection Rate is taken (as shown on the diagram above) and the corresponding Liquid Rate calculated from the well response. This rate will then be used to calculate the response of the surface pipelines that will return a new Well Head Pressure, based on the pressure drops in the system. A new Performance Curve will then be constructed for the well (again based on the new WHP kept constant):

The iterations are then repeated in order to converge to the solution:

Even in this simple system, things will not behave in this way in reality. Each time a guess on Gas Lift Injection rate is taken, the pressure drops in the pipeline will cause the back pressure on the other well to be different.

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This system is by nature Non Linear and is conceptually similar to the function described earlier. Linear programming techniques will not be able to see the impact that gas injected in one well will have on the other due to the pressure drop in the surface lines. The true response on a well is shown below:

This response can only be captured by the NLP method. SQP (Sequential Quadratic Programming) techniques work by calculating the response of every element in the system, not only on how pressures will change with changing flowrates, but also how the gas lift gas injection rate will impact the pressures. As these responses are inbuilt in the calculations, the actual behaviour for the wells can be constructed and the optimum solution found as shown in the last figure. NLP will always result in higher rates with less gas injection compared to Linear Programming. PRODUCTION OPTIMISATION USING GAP

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About This Guide The guide generally assumes that the user is familiar with basic Windows operations and terminology; if the user is new to the Windows system; refer to the operating system user’s Guide. GAP, along with other Petroleum Experts software, can comfortably be used under Windows 98, Windows ME, Windows NT, Windows 2000 and Windows XP operating systems. The screen displays in this guide are created using a Windows XP interface. The screen displays used in this guide are taken from the examples provided with the software as well as models from clients (with permission). On occasion, the data files may vary from the examples shown as updates to the program are issued. Where major amendments or changes to the program require further explanation, the corresponding GAP User Guide

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documentation will be issued.

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1.10 Examples Index The following table can be used as reference for the example included in this Guide. Application area

Topic Examples Guide Setting up a network model for a gas Gas field Modelling and Example 1 535 field, entering constraints and Optimisation Schedules, running Predictions Setting up a network model for an oil field, Model Validation to QC the well models, using "Initialise IPRs from Oil field Optimisation and Tank Simulations" to update the Example 2 574 Forecasting model to a certain time, setting constraints, running Solve Network, entering schedules and running Predictions Viewing details of the pressure drop Detailed results for Example 3 619 calculation in GAP using PROSPER on pipelines line feature Setting up a network model with gas lifted wells, pipeline pressure drop Artificial Lift Modelling and Example 4 628 matching, gas lift optimisation using Optimisation GAP Optimisation feature, use of the well Controls Generating lift curves for gas lift wells with casing head pressure, setting up a network model for the gas lift Gas lift injection network Example 5 654 injection network, linking the optimisation production network to the injection network and optimising the two coupled network models Setting up network model with ESP lifted wells, Model Validation to QC well models, Pipeline Matching to Artificial lift Optimisation Example 6 678 validate pipeline pressure drops, Model QC running Optimisation to honour constraints on maximum power available Setting up network model for water injection system, linking it to the main Pressure support with Example 7 709 production model and running water injection Prediction with the two coupled models Using PROSPER on line to run Flow assurance studies on Example 8 724 advanced temperature modelling in pipelines pipelines, importing PROSPER GAP User Guide

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Modelling surface equipment Smart well completions

PVT Compositional modelling PVT Compositional Lumping/Delumping

PVT Black Oil Compositional Lumping/ Delumping

pipeline models in GAP Modelling de-hydration and heat exchangers with the Inline General (or Programmable) element Setting up a network model for a multi-layered well completion with inflow controllable valves, optimising the two layers to maximise oil production Setting up a GAP network model for a gas retrograde condensate field using the fully compositional method, running predictions and evaluating the changes of composition Exporting the lumped and de-lumped compositions from PVTP, setting up a GAP model with compositional lumping/delumping, running model and viewing the results Setting up GAP to work with Black Oil Compositional Lumping/Delumping, running model and viewing the results

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Example 9 737

Example 10 743

Example 11 761

Example 12 795

Example 13 816

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1.11 What's New

Version 8.5 The main new developments implemented in GAP version 8.5 are: PVT Modeling Gas viscosity correlations (Lee et al. and Carr et al.) selectable for pressure drop calculations Pipeline Modeling Advanced temperature modeling (Improved Approximation) available along with the default GAP Internal Correlations pipeline modeling Modeling of condensed water vapour in pipelines with GAP Internal Correlations pipeline modeling Well Modeling Liquid injector well type to model for example polymer injection HSP wells VLP format with sensitivity on pump speed Well Control ∆T through dynamic well control choke is now accounted for Displaying Constraints Violations Setting option to report violated/limiting constraints when running with no optimisation Program Interface GAP User Guide

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Possibility to select all the elements belonging to a Group PVT Model displayed in tanks

Version 8 The main new developments implemented in GAP version 8 are: Fluid Modeling - Compositional an Black oil modeling Lumping/Delumping methodology – Compositional Lumping/Delumping – Black Oil Lumping/Delumping Speeding up of fully compositional models Process independent VLP's and IPR's with MW and Mass Al-Marhoun correlation for Pb, Rs & Bo Egbogah et al (heavy oil) correlation for viscosity Import .PRP composition file for multiple wells, main PVT and Gaslift PVT Modeling Gas Lift Injection Network Generation of IPRs from PROSPER for Multi-Layers wells or Inflows Automatic setup of MultiLayer wells from a PROSPER files Model flare and vent in GAP and capture in reports as "emissions", with different revenue and separate category in Reports Option to turn wells off if the intersection of VLP/IPR is left of the minimum. Performance curve points increased to 20 Add outputs of energy, for production and cumulative production, to get output in units of kilo-watt hours (heating value x mass)

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State the correlation used to generate pipeline VLPs on the VLP page Option to switch on / switch off pressure drops in pipelines (e.g. bypass on pipelines) Automatic transfer of the latest well test data on Matching screen from PROSPER into GAP Model Validation screen Option to use Lookup tables for fractional flow instead of relative permeability curves Option to populate decline curve tanks and related wells production data tables from prediction results. Oil injection manifolds Oil rate abandonment constraints Option to use WGR in tight gas wells Program Interface Different icons for dp control and artificial lift control Different colour coding for constraints and abandonment constraints Schedule clock icon visible for masked items Display GOR, WCT, CGR, WGR, dP and dT in Tooltip box Display current operating point on compressor performance curves plot Default Unit System can be set up in preferences

Version 7.0 The main new developments implemented in GAP version 7 are: Modeling Internal steam calculator Improvements in the inflow performance models GAP User Guide

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Gravel Pack modeling Ability to model a well with layers having different fluid types Tight Gas Wells Well modeling: Include WGR for gas injectors Pipeline modeling: Annular flow calculation Improved Approximation temperature model for Steam Specify Black Oil Correlation for each Pipe Element Compressor modeling: reciprocating compressors Simultaneous Water And Gas Injection modelling Prediction: DCQ contract type: gas rate, gross heating value... DCQ prediction New event schedule, such as ESP frequency... Schedule Event Grouping OPENSERVER access variable scheduling New constraints, such as temperature constraints, tank withdrawal constraints... Program Interface The GAP user interface has been updated significantly. Edit/Undo button Copy, Cut and Paste of selected network items Flowsheets (sub-models) GAP archive - option to create a new folder Display pipeline gradient calculation's results Permit models to be run minimized on a PC Allow user to add comments on main GAP screen Enable facility to plot multiple scenarios 1990-2011 Petroleum Experts Limited

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Add plot to total field system recovery factor More consistency between screen buttons (i.e. "main", "done"...) OPENSERVER: wildcard option "@", i.e. Well[{@W*}] Visualization of limiting/violated constraints Ability to view schedules of equipment at same time Ability to cross check well definition in PROSPER Allow user to move element name in GAP graphical view Ability to view Solver Log or Prediction Log directly Ability to add elements to a Group using the 'Add Link/Pipe' Option user can now specify flow correlation to be used when generating Lift Curves for Pipes. user can now view all elements linked to a GROUP from the same screen.

Version 6.0 GAP Fully Compositional All PVT calculations are performed using EOS models. In this version the fluid can be described using EOS and the calculation are based on the individual EOS response. Better modeling of fluid such as Retrograde Condensate and critical fluids. Account for condensate dropping out of gas. Three Levels of optimization to speed up the calculations. Major improvements in speed of EOS calculations The process is shared with MBAL and PROSPER Now the entire field response can be modelled using EOS model in the three programs / GAP / PROSPER /MBAL Modeling GAP User Guide

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Diluents Injection in wells and pipelines. HSP and Jet Pump lifted wells. Surface Jet Pump in pipelines. These models have the following characteristics Injected fluid is modelled through tables Choice of fixed or optimized injection rates Well modelled with lift curves or PROSPER online Other General enhacements IPR includes the bubble point as part of the data for matching the IPR Now if the bubble point of a test is available it can be used with the matching information to adjust the IPR. Fitting available for pipeline description Different fitting elements such as valves, conections , elbows etc can be modelled in the pipes as an equivalent length and be accounted for pressure drop calculations. Increase to 100 segments for pipeline description Under the pipe description up 100 hundres rows are now available to describe pipe geometry. The number of fields for pipe description is not longer limited to 25.

Allow CGR and WGR input in gas fluid calculations When a gas is defined as a new fluid under the fluid injection screen now there is the possibility of specify the CGR and CGR . A new overall equipment control screen a new summary screen equipment controls had been introduced. This will allow from a centralized screen evaluate all the equipment that have been controlled in the system New Open server commands

Version 5.0 Program internal structure Memory Management Enhancement This release uses on average nine times less memory by avoiding any memory wastage. All tables use dynamic memory allocation, creating records only if required. 1990-2011 Petroleum Experts Limited

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Structure Enhancements There is no program limit to the number of pieces of equipment contained in a model. The number of ipr's in a well is not longer limited to 30. Enhanced validations Data validation routines have been enhanced to trap data input errors before calculation starts. Invalid fields are highlighted in red in the screens. Network TVD validation The program highlights the joints where TVD inconsistencies occur. If necessary, this feature can be turned off using the 'View', 'Highlight TVD differences' menu option. Enhanced Open Server support The program supports enhanced open server expressions such as GAP.MOD[{PROD}]. WELL[$].DPControl where the $ sign means ALL ( see the Open Server manual for more details). For example, to set the dp control of all the wells to 'Calculated' the following open server statement can be used : GAP.MOD[{PROD}].WELL[$].DPControl = CALCULATED. To set the dp control all the wells of all the models use the following statement GAP.MOD[$].WELL[$].DPControl = CALCULATED. Prediction results are saved to disk All prediction results are saved to disk while the prediction is running. This makes the program memory requirement independent of the number of prediction steps. Purge of prediction snapshots and results All prediction results can be cleared to reduce the data file size through the 'Prediction', 'Purge All Prediction Results' menu option. Program interface Internal solver and prediction message log sorted by type The messages generated by the solver and the prediction runs are saved to disk and sorted by type i.e. Log, Errors, Constraints, Events, ... Internal OPENSERVER editor An OPENSERVER command editor is available under the 'Edit', 'Execute Open Server Statement' menu option. This allows the user to send OPENSERVER messages to the application without the need of an external application. For example to make all the wells controllable, the GAP.MOD[{PROD}].WELL[$].DPControl = CALCULATED command can be executed from within GAP. Customisable dialog size Dialogues with the 'sizeable window' pattern in the bottom right corner of the window can be resized by the user to fit their screen resolution. Holding the Shift key down while GAP User Guide

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opening the dialogue will reset its size to its original value. Convert well into inflow or split well into inflow and outflow Existing wells can be split into an outflow only well (VLP) and inflow pieces of equipment. Main screen equipment locator while editing While editing the pieces of equipment, double click on an icon on the main screen to edit that piece of equipment. Main screen information displayed customisable The 'View', 'Select Info Displayed' allows the user to select one parameter that will be displayed along with the label on the main screen graph. Modeling Downhole Networks Outflow only well and inflow pieces of equipment allow the modeling of 'smart' wells. Any piece of equipment (joints, pumps, separators, pipes or completions ...) can be inserted between the inflows and the wells. Outflow only wells (smart wells) with VLP or PROSPER online Outflow only well can be modelled using lift tables or PROSPER online. New ways of modeling pipelines - VLP and PROSPER online Pipelines can be modelled using GAP internal correlations, lift tables or PROSPER online. Internal lift curve generator for pipeline GAP includes an internal lift curves generator for pipelines. GAP uses its own internal flow correlation or the PROSPER online model to generate the lift curves. PCP lifted wells Progressive Cavity Pumps lifted wells can be modelled. The motor speed is available has optimisation variable. PVT impurities from composition When run enabling the compositional tracking option, the black oil pvt impurities mirror the composition impurities IPR permeability correction due to compaction Pemeability correction for compaction effect is available in the ipr description screen. Revenue, Cost and Tax Regimes The user can define multiple 'Tax regimes' (i.e. revenue and cost prices) and assign them to wells, inflows and sources. 1990-2011 Petroleum Experts Limited

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Equipment Grouping Individual pieces off equipment can be assign to one or several groups even if these pieces of equipment are not related or connected together. The groups can then be assigned rate constraints Computation Faster and more robust Solver and Optimiser Potential calculation in solver and prediction runs When requested to do so, the program will compute the field potential by removing all the constraints and running an optimisation. Optimisation on revenue Riser gaslift gas included in revenue calculation More robust compositional tracking

Prediction Material balance and decline curve prediction types have been merged Decline curves and material balance reservoir models can be associated in the a prediction run. Internal prediction Visual Basic script Under the 'Prediction', 'Edit Prediction Script' menu option, an internal visual basic script is available to dynamically control the prediction run. IPR WCT or GOR versus cumulative production for decline curve tank WCT and GOR profiles can be entered versus cumulative production or reservoir pressure. Prediction results and network snapshots are saved during prediction runs through OPENSERVER

Note: The GAP sample files are distributed as archives (which contain all the files necessary GAP User Guide

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to run the models). For a quick description of how to extract the sample files, click here. Note on Open Server GAP can be operated or automated from other applications, for example through the writing of spreadsheet scripts in Excel or Access. The potential uses range from Simple importing and exporting macros through Interfacing GAP to other modeling applications such as reservoir and facilities simulators. A powerful feature is the ability to perform predictions in a step-by-step mode, allowing Data Server macros to be run at each timestep. This can be used to implement, for example, event driven scheduling (changing IPR during a prediction, changing constraints with time, overriding the GAP optimiser, scheduling compressors...)

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2 User Guide 2.1 What is in this guide? A flow chart which outlines the basic procedures required to carry out a full field network optimisation study using GAP is shown on the last figure. The organisation of the manual adheres to the GAP processing logic as outlined by the flowchart as much as possible. Introduction 39 Getting Started 44 with GAP 44 Describing 124 the PVT 124 Equipment Data 149 VLP/PR 39 Generation 39 Model Validation 425

Network Solver 434 and Optimiser 434 Prediction 453 Results and 494 Reporting 494 History Matching 510 an IPM Model 510 Prediction Script 520 Defining 525 System Units 525

Introductory information on GAP and the user Guide General information on the usage of GAP This section describes the PVT modelling options available in GAP This describes the interface used for entering equipment data, and describes in detail the data entry screens for all elements This section shows how to generate VLP/IPR using PROSPER for inclusion in the GAP system model This section introduces the user to the Model Validation menu option in GAP, which allows efficient quality checking of the well models in GAP This section describes how to solve network and check that model production matches actual production This section describes the coupling of reservoir tank models to GAP for production forecasting This explains how to prepare, print and plot the results General steps to follow to make sure that the model is calibrated and representing reality Section describing the scripting features present in GAP This section describes how to set up Unit systems in GAP

. . .

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2.2 Introduction Petroleum Experts General Allocation Package (GAP) is an extremely powerful and useful tool offered to the Petroleum Engineering community. Some of the tasks GAP can achieve are: Complete Surface Production / Injection Network modeling. Optimisation GAP has a powerful optimiser that is capable of handling a variety of wells in the same network Naturally flowing oil wells Gas-lifted wells ESP operated wells Condensate or gas producers Water producers Water or gas injectors PCP wells HSP wells The Optimiser controls production rates using wellhead chokes, ESP operating frequencies or allocating lift gas to maximise the hydrocarbon production while honouring constraints at the gathering system, well and reservoir levels. Allocation of Production Predictions (Production Forecast). GAP models both production and injection systems simultaneously, containing oil, gas, condensate and/or water wells to generate production profiles. GAP’s powerful optimisation engine can, for example, allocate gas for gas lifted wells, alter the frequency of ESP pumps or sets wellhead chokes for naturally flowing wells to maximise Revenue or Oil Production while honouring constraints at any level. GAP can also model and optimise injection networks associated with the production system (both together). Production Forecasting GAP calculates full field production forecasts including gas or water injection volumes required to meet reservoir unit pressure constraints.

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Reservoir pressures are obtained from decline curves, material balance or simulation models. The associated injection systems can be modelled and optimised so as to achieve injection targets for pressure maintenance programmes. Link to third party tools via OPENSERVER GAP has an Open Architecture that allows Third party software to exchange data with GAP. Run and control GAP via the OPENSERVER technology developed by Petroleum Experts Link to MBAL Reservoir performance for production forecasting is provided by links to Petroleum Experts’ MBAL material balance program. Fully coupled production and injection (gas and water) models can be solved by GAP with optimisation of production and calculation of injection pressures at every time step. Link to PROSPER Well performances for production forecasting are provided by links to Petroleum Experts’ PROSPER, the single well model package within the IPM Suite. PROSPER can be run in a batch mode from GAP for generation of well performance and lift curves for simulation. Fully Compositional or Compositional Tracking Modes GAP can calculate the PVT fully compositionally and track compositions from the well/source level through to the separators. In a prediction, GAP can take compositions calculated by MBAL and record the evolution of compositions throughout the system with time. The compositional tracking can be done as in previous versions using the BO model. Lumping/delumping of compositions can be performed in both the fully compositional and black oil cases

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2.2.1 How to Use This Guide Depending on the modelling needs and the amount of time the user wants to spend becoming familiar with the program, the user guide can be used in the following ways: Beginning-to-end If the user is new to Windows applications, we recommend to read this document from beginning to end to become familiar with the program features, menus, and options. This is the slow approach, but will cover all is necessary to know about the program. Selected tasks Use this approach only if the user is already familiar with the basic functionality of the program. Worked examples If the user has limited time and want to sample the program features quickly, follow the instructions provided with in the examples. The examples can be found in the Examples Guide 531 . The examples show how to build a network, run sensitivities and perform a prediction run with a reservoir model attached to the surface network.

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2.2.2 GAP Glossary of Terms The following table introduces some key terms in network modeling using GAP. Term

Application

Abandonment Value

For Prediction runs only. Minimum rates, maximum GOR etc. can be set to turn wells off.

Actual

Evaluation of well models for specified top node (wellhead) pressure, GOR and water cut. Used to quality control well models by comparing model and actual measured test rates.

Compositional Tracking 142

The tracking of fluid components/compositions from the well bore to the top (separator) node.

Constraint

Constraints are used to direct the GAP optimiser to honour process limitations, limit well production rates. Minimum constraints can give a flow stream priority when optimising. Constraints always refer to GAP optimiser. Well abandonment rates are set elsewhere.

Element

A well, joint, pipe, separator, tank etc. used to construct either production or injection systems.

Generate

The process of calculating and importing well parameters like IPR VLP

GOR

Gas / Oil Ratio. In GAP this is the Producing GOR including solution and free gas, but excluding gaslift injection.

Icon

Graphical symbol used to represent a system element.

IPR

Inflow performance relation. Function relating pressure drop across reservoir and production rate. IPR s can be generated directly from PROSPER.

Node

Point where one or more production elements connect to another system element.

Performance Curve (PC)

Curve representing the well response as pressure downstream the well (or manifold pressure) vs rate produced. The PCs can be generated from VLP/IPR by sensitizing on well manifold pressure for a given reservoir pressure and content of water and gas (respectively, water cut and GOR)

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Pipe

Pipes connect joints together to form a gathering system. Pipes in GAP have a length, elevation, inside diameter and roughness.

Prediction

Calculation of (optimised or not optimised) future production and injection rates using pressure decline curves or reservoir models (MBAL for instance).

Production Allocation

Use of systems analysis models in GAP to calculate field and well production rates for specified reservoir and surface pressures given the current water cut and GOR.

Production Optimisation

Process of maximising oil/gas production (or revenue) by adjusting wellhead pressure/gaslift injection/ESP frequency while simultaneously honouring constraints at various points in the system.

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Solve Network The process of calculating the combined production response for the entire production system.This can (optimised) be coupled with the optimisation process, allocating the gas lift gas and the power available to optimise the overall system production or injection. Tank

VLP

A reservoir unit. It can be modelled rigorously with MBAL. It can also be represented by a table, relating pressure and cumulative oil production (decline curve option). Vertical lift performance. Expression relating surface well pressure and bottom hole pressure.

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2.3 Getting Started with GAP For first time users, this chapter covers the essential features of data management and setting up the calculation options of GAP; in essence, everything one needs to get started on a GAP project. The chapter starts with a description of the user interface. A step-by-step guide to starting a GAP project from scratch follows this. Menu options will be considered in this Chapter, although some will be discussed in more detail in later chapters when their use will be put in context of an actual model.

2.3.1 The GAP User Interface The main screen of GAP has the following structure:

The user interface consists of a framework window that contains several child windows, as well as the menu and toolbar from which GAP commands are issued. The child windows GAP User Guide

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include the system windows that contain the system network drawing, and the navigator window that can assist in the viewing of large networks. The interface consists of four parts, as indicated in the figure above: System window the window on which the system network is drawn Navigator window contains a full schematic which can be used to help navigation about large systems Toolbar contains menu accelerators, icons for selecting and manipulating system equipment, and icons for zooming or un-zooming on the system window Menu usual menu for issuing commands to GAP Menu functions are discussed in the following chapter. The other three parts of the interface as listed above are described in the sections below.

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2.3.1.1 Opening a File When GAP is opened, if the preferences have not been set up to open the last file accessed, there will be a blank system view. To open a GAP file at any time during any GAP session, select File Open. The following screen will be displayed:

This is the standard Windows file browser, which may be familiar with from other Windows applications. The dialogue box lists the files that match the selection criteria on the left-hand side. The files in the default working directory are automatically shown first. Double-click on the file name required and this will be opened by GAP. The Open as read only option enables to open a file as a read-only file, which can therefore be consulted but not modified.

2.3.1.2 Saving a File When files are opened in GAP, a copy of the selected file is stored in computer memory. Any changes to the file are made to the copy in memory. In case of a power failure or a computer hanging up, these changes are completely lost. To maintain the present work, we recommend to save the data on a regular basis. This simple procedure could potentially prevent hours of work and analysis being lost. To save a file, choose either File Save or File Save As. The Save command stores changes made to the current active file, overwriting the previous data. By default, the Save command saves a file under its original name and to the drive and directory last selected.

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2.3.1.3 The System Window The system window is the main window on which the GAP network is displayed. More than one system window can be displayed in GAP at one time; this means that different views of the same system or production and injection systems can be viewed simultaneously. An empty system view window is shown below:

The system window is used to draw, edit, and view the system. Coloured icons represent the equipment nodes. The different actions that can be performed on this window are obtained by clicking the right hand mouse button within the area of the system window. This brings up a menu, as shown on the screenshot above. Alternatively, the same set of actions can be performed using the toolbar or the menu, which are described below. Addition of Network To add an item to the system, activate the required equipment type from the toolbar or use the right hand mouse button. The cursor Equipment appearance on the screen will change to indicate that an equipment selection has been made. Click on the screen at the point where the equipment is to be inserted. A network node will be created, and a label dialog will appear prompting to name the new equipment.

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Zoom In / Out

To zoom in or zoom out, first select the appropriate icon from the toolbar or from the right hand mouse menu described above. To zoom in on an area, hold the left-hand mouse button while sweeping the mouse cursor over the area of interest. Alternatively, one may click once at a point in the system, and GAP will zoom or un-zoom on that point using a fixed scaling factor (which may be adjusted using the Preferences dialog).

To revert to a full system view at any time, double-click the left-hand mouse button at any point in the window (except on an equipment node). The view will rescale to show the whole of the system. Selection of Items To select an item or items, first select the select icon from the toolbar or from the right hand mouse popup menu. Click on the item to select, and its colour will reverse accordingly. Alternatively, dragging the left-hand mouse button over an area can make group selections. Masking / To mask or unmask an item or items, first select the Select icon from Unmasking of Items the toolbar or from the right hand mouse menu. Click on an item to mask or unmask it: if equipment is masked, all child items will also be masked. If a piece of equipment is unmasked, parent items will be unmasked to allow a production path to the top node. To mask or unmask a group of nodes, the left hand mouse button may be dragged over an area of the system view. Deletion of items

Select the delete icon from the toolbar or from the right hand mouse menu. Groups of items may be deleted as above. Right hand Mouse Utility menus will appear when the right hand mouse button is clicked anywhere in the system view. The normal menu is displayed above, and Button Actions appears when the button is clicked over an empty space. If it is clicked over an equipment node, a shorter menu will appear with a number of equipment specific functions, such as delete, mask, or select. Panning To move the view around the system, simply click on the main window and hold the left mouse button down. Shift the mouse and the network will be moved following the direction of the mouse movement. Popup Status As the mouse is moved over equipment nodes, a small window will appear. This contains basic status information for the node in question Information and allows the status of a piece of equipment to be checked without entering the data entry screen. This is optional: to switch this function off go to the Preferences screen and un-tick the “Enable Flyover Status Information”. Changing Icon These functions are also available from the right hand mouse menu as well as from the main menu under Options. See below for more Sizes / System information. Fonts Title Bar This indicates whether a production or injection system is being viewed. Opening a New It is possible to open a new GAP window specifically focused on one GAP Window area of the network. To do so, zoom on the system region to consider and click the Shift key after the zoom region as been specified. A new GAP User Guide

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GAP window will then be opened. specific Minimise: Click this button to minimise the window in the GAP workspace. Maximise: Click this button to maximise the window to fill the GAP workspace. Following this, if GAP is shut down and restarted, it will automatically bring up the new window in a maximised state. Close: Click this button to remove the window from the workspace. Restore: This restore the default system window

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2.3.1.4 The Toolbar The toolbar is located below the main menu at the top of the main window. It consists of a row of icons (described below) which act as accelerators to common menu functions, or allow the addition or manipulation of network icons in the system window.

The functions of the various buttons are described below. File/Interface Functions Accelerator for File | New. Clears the current system and initialises a new one. A warning will be displayed if there are any unsaved changes in the old system. Accelerator for File | Open. This will prompt for a new file name. If the file can be opened successfully, the old file will be cleared and the new file opened in a new window. Accelerator for File | Save. By default, this will override the currently saved version of the file. Use File | Save As to save the file to a different location. Accelerator for Window | New Window. This will open a new full system view of the current file. System Functions Accelerator for Equipment Control / Model Validation screen Accelerator for Network Solver. Accelerator to access script Accelerator for Prediction | Material Balance Forecast. This initialises a material balance or decline curve prediction, depending on the system mode as set up in the Method

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screen. Equipment Set-up When an equipment button is selected, click once on the system window to create a new node of the required type at the chosen point. A label dialog will appear to allow equipment to be labelled immediately. Add a separator. This is the final solution node and is located at the "top" of the system, i.e. furthest from the wells. GAP will optimise the entire system connected to all separators. The separator does not have to be an actual one. In GAP, separator is a convenient way of describing a point of known pressure in the network. For injection systems, this button will add an Injection Manifold. Add a joint. This represents a network node. A joint is a solution point in the system. Add a link. Note that this can become a pipeline, a well-tank connection, or a pump connection depending on the context of the connection being made. Add a well. The default well type is oil well, gas lifted (unless in an injection system). The well type can be changed from the main data entry screen. When drawing well icons, it is suggested that they are arranged around the connection point. This simplifies the drawing of the pipeline connections. Add a tank. This represents a reservoir source. Tanks are only required when running predictions. Add a flare or vent. This element withdraws from the system a fixed rate of fluid Add a pump. A pump is associated with a joint or separator. If associated with a joint, it is in line with the joint, between the joint and the pipeline connecting the joint to the next level. Add a compressor. A compressor is associated with a joint. If associated with a joint, it is in line with the joint, between the joint and the pipeline connecting the joint to the next level. Add a source/sink. A source/since is created and should be described. A source/sink can be at fixed rate or a programmable element. Add an inline element is created. This can be an Inline Gate Valve, an Inline Check Valve, an Inline Separation, an Inline Choke or an Inline programmable. Add inflow, when this option is selected, it will contain similar data as the well except that do not include the VLP’s. This 1990-2011 Petroleum Experts Limited

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icon is used essentially for downhole networks. Add group, using this option the same constraint can be applied to certain groups of wells. Add flowsheet, creates sub-flowsheets that can be attached to the main GAP flowsheet Zoom in/out. When 'zoom in' is selected, a zoom can be achieved either by clicking the mouse on the system window, which will zoom in a fixed amount and set the centre of the view to the position clicked, or by sweeping an area with the mouse which GAP will then view. The aspect ratio will be retained when an area zoom is performed. Mask / unmask. When either of these are selected, clicking on an equipment item in the system window with mask or unmask the item as directed. For short-term removals of equipment, this is to be preferred to deletion, which removes the equipment permanently. When masking, all child nodes will also be masked. When unmasking, parent nodes will be unmasked so as to clear a passage to the top-most node. From GAP version 4.0 onwards, any masked item will be brought online by Schedule during prediction. To exclude any item from prediction (irrespective of what is set in the Schedule), use Disable / Enable. This Icon will disable completely any item in the production / injection system during the production forecast or solver network calculations although the item is set to run with certain schedule. This Icon will enable any element in the production / injection system. Delete. After this is selected, it is possible to delete a node by clicking on the item in the system window or delete a whole section of network by dragging a box around it. The icon automatically becomes unselected following a deletion to prevent accidental deletion of further nodes. Move a node. After this is selected, a node may be moved by clicking on the item in the system window and then, with the mouse button depressed, dragging the item to the new position. Select a node. After this is pressed, a node may be selected by clicking on the item in the system window. The item will reverse its colour to indicate selection. One can select any item on the window system for further actions: set wells to controllable, move items, delete items…

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Unselect all items. Find/locate equipment on the System window. Use this option to locate equipment on the system window. This may be useful in large systems in which the icons are close together and whose labels are therefore difficult to read. Help Index/Accelerator. Use this option to access the online help index. A database will allow to make guided searches by entering keywords in the provided screen. Undo button. This button allows to undo the actions taken when building/modifying the model

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2.3.1.5 The Navigator Window To activate the navigator window select |Window |Toggle Navigator Display (see hiding/ showing the navigator described below). This window can be used to aid in navigation about a large system. It will always consist of a system schematic that is independent of any zooming on a system window. In addition to the network, it contains a tracking rectangle that encloses the portion of the system currently under view in the system window. Other functions are possible, as described below.

Tracking Rectangle

This has two functions. If the focus is currently on a system window, this rectangle surrounds the area of the system that view is displaying. Alternatively, the rectangle may be used to create new views of the system if the navigator window is currently in focus. When the mouse is moved over the rectangle, the cursor changes to allow to stretch or resize the rectangle. In this way the window may be moved over an area of the system of interest. Double-clicking the left hand mouse button in the area will create a new system view displaying the area that has been selected. This is resized to preserve a sensible aspect ratio Hiding/ The navigator may be removed from the workspace by clicking on the cross Showing the button at the top right hand corner of the window. Alternatively, the Window menu item of the main menu contains a function to do this. Once removed, the Navigator navigator will not appear in subsequent GAP sessions until reopened. This can be done by clicking on |Window |Toggle Navigator Display as below

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Right Hand Clicking the right hand mouse button within the navigator window will produce Mouse Button a utility menu. This contains the following functions Menu Navigator on By default, the navigator is always on top of all system views. This can be changed by selecting this item from the menu Top Hide Window A different way of hiding the navigator New Window A different way of producing a new view (see above) Icon Sizes Invokes the Icon Sizes dialog (see below) File Options In this section, the user defines certain parameters, which control the normal Windows functionality of the program as well as preferences

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2.3.1.6 Drawing the System The following section describes the procedures required to define a system network topology. This is done by manipulating graphical icons to draw a system schematic diagram. Once the basics of drawing a system is understood, building a GAP network model will take very little time. The GAP system network is based on a series of elements accessible from the program Toolbar. The Tool Bar The GAP tool bar contains a button for each element that can be added to a system network. An element can be placed anywhere on the screen, and its position on the screen does not affect the program calculations. To select an element, press the appropriate button to activate the object. To draw the element, position the mouse pointer anywhere on the system view and click. A 'Label' dialogue box appears to name or identify the icon. Data for each element can be entered as the system is built, or once the entire system have been finished. When the data is entered while building the system, double-click the appropriate icon to access the main data entry screen. The following tool buttons are used to draw a system: Separator

Adds a production separator. This is a point in the system whose pressure is known and fixed. This is the final solution node and is located at the "top" of the system i.e. furthest from the wells. GAP will optimise the entire system connected to all separators. Joint Adds a manifold joint or connecting point in the system. A joint is a solution point in the system. Connecting two joints creates a pipeline Add Link/Pipe Creates pipelines between manifold joints and other joints and links between separators and joints manifolds to wells, tanks to wells and joints or separators to pumps. Short flowlines are best modeled as part of the well rather than as a pipeline. The type of link produced is decided from the context of the link. To link two items, activate the link icon. Click on the first item in the system view, and drag the mouse to the second item with the mouse button depressed. When the button is released a link will be produced if the context is valid Well Adds a well in the system network. When drawing well icons, it is suggested they be arranged around the connection point. This simplifies the drawing of pipeline connections Tank Adds a tank in the system network. These may be modeled separately using the MBAL software which can be supplied by Petroleum Experts Flares and Adds a sink at constant rate of pressure and the amount of fluid collected by them is accounted for in the emissions results Vents Pump Adds a pump in the system network Compressor Adds a compressor in the system network

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Adds a source or a sink that injects/withdraws a fixed amount of fluid of a user-defined fluid Adds a choke, inline separator, valve and virtually any piece of equipment that can be described by a script Adds an inflow element (IPR), which can be used to model complex well geometries by decomposing the well into inflows and outflow Adds a group element, which is used to report or impose constraints to groups of elements in the GAP network (for example, clusters of wells can be grouped together) Allows to place whole sub-sections of the main model into different flowsheets. Particularly useful in the case of big models, where the flowsheets allow to simplify the model view

Drawing elements The first thing to consider before drawing a system is its layout. For instance, the number of elements to include can determine how to design the structure. A brief outline or sketch of the network may help deciding how to plan the model. Since the key solution point in the network is the separator, one way to proceed is starting at the top with the separator(s) and working down through the manifold joints (incoming connection pipes) to the wells. 1. To draw an element on the screen, the appropriate object on the tool bar must be selected. Positioning the pointer on the screen and clicking the Left mouse button will place the element on the desired position. (When drawing a system from scratch, start at the top and centre of the screen and work down and outward is suggested 2. When the element is placed on the screen, a dialogue box will automatically appear where the label of the element can be entered. Labeling is optional, however typing in a short name or abbreviation to identify the element icon is suggested. Click the OK button or press Enter to return the screen display 3. Select the next element to draw by clicking the relevant button on the tool bar. Position the pointer on the screen where you want to place the element and click. A dialogue box will appear prompting to label the element again. Follow these steps for each required element 4. It is recommended to build a system gradually until a grouping of elements provides the basic framework. To begin, it is not necessary to have a definite layout in mind as the program easily allows modifying or add elements to the system 5. When all the elements have been set on the screen, select the Add Link/Pipe tool and connect the element by dragging and dropping a line between each couple of elements starting from the element that is upstream the flow direction. This will create pipelines (when linking two joints) and connections

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New elements to the network can be added until the created a system reflects the actual conditions or have adapted the structure to suit the particular requirements of the project. Entering data Once the icons had been placed and labeled, the data for each item need to be entered. The properties of an item can be entered as they are added to the system, or later when the complete network model has been graphically laid out. To enter data, double-click on the corresponding icon to be edited. The main data entry screen for the element will appear. From this screen, other elements in the system for data entry can be selected. Duplicating items GAP includes a utility that allows copying element items. This facility is useful if adding many elements of similar properties (e.g. wells), as it can save time entering data when editing the item(s). When copying an icon, the program makes an exact duplicate of the item, which includes the PROSPER file name, data and icon label. To duplicate icons two ways are available: 1. Point the element to copy, right click of the mouse and select "Copy". Point the location where the new element is to be created and then right click again and select "Paste" 2. First draw or add a new element icon. Do not label the new icon. Next, copy the data from the original element icon to the destination unnamed icon. To copy, hold down the 'Ctrl' key, while clicking and dragging the original icon into the new unnamed icon. Data from one element cannot be copied into another element type. That is, the data of a Separator icon cannot be copied into a Joints icon. For more information on the user interface and its use, see The GAP user Interface.

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2.3.1.7 The Preferences Dialog The preferences dialog allows a set of user-interface variables to be customized for subsequent GAP sessions. Some of these options are self-explanatory so a limited description is given below.

Enable Flyover If this is checked then it will be possible to see a status box appear as Status Information the mouse pointer goes over the equipment icons Auto-repeat delay When panning, one may hold the left-hand mouse button down to ‘autorepeat’ the action. The value given in this field represents the time (in ms) when panning before the auto-repeat action starts from when clicking the mouse button Zoom/UnZoom A single click in a system window while the zoom or un-zoom icons are active results in a fixed scaling to be applied to the view, while the centre factor

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of the view is changed to the position in which the mouse was clicked. The value entered in this field is the fixed scaling factor, and as such should be greater than zero Open server When GAP is run using the open server functionality, there is the option Monitoring of displaying the results of all the open server commands in the Open server Monitor Window. The option allows this window to be shown / Window Hidden Background The bitmap that is displayed on the background of the main window may be changed (i.e. by default this is a PE logo with contact information). Select the required bitmap by pressing the browse button to the right of the field. The bitmap will be loaded when GAP is restarted Recent file list This is the number of files that are retained at the bottom of the File menu length Reload last project Check this to load the last file that was working on when GAP is started at start-up Display “Alter If checked, GAP will check all files paths once a file is opened and will Project Paths” allow the user to correct these if needed prompt at load time License Handling – With the “PROSPER on line” options added to GAP for Version 5.0 or VERY IMPORTANT later, licenses of PROSPER and/or MBAL may be used by GAP depending on the options chosen when building a model. It is recommended to keep these options to the default. Please consult with the person in the organisation responsible for license handling before changing any of these options Default Input (and This option allows to set the default units systems for GAP model for Output) Unit either input or output variables. This unit system will be used whenever a new GAP model is built System Always Use Ticking this box will force the unit system to be the same as the default one. If a GAP model contains different units to the default, when opening Default Unit the file, GAP will change the units to default System

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2.3.1.8 Defining User Correlations GAP has the facility to use externally programmed pipeline flow correlations. Before they can be accessed, they must first be linked into GAP. To use external correlations, click File user correlations | Flow Correlation. The following screen will be presented:

Click Add and select the required .COR correlation file from the browser. The Info button can be used to examine details of the selected correlation. Click OK to return to GAP. The external correlation will now be available for calculating pipeline/tubing pressure drops. Please contact Petroleum Experts to obtain more details about the multiphase DLL format required to create the *.COR files. The Remove button removes the selected correlation from GAP. It is not possible to remove the GAP internal correlations.

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2.3.1.9 Edit Ini File The Ini file is a text file in which all the preferences for GAP are stored. Some of these are the directory preferences, colours, tolerances etc. It is recommended not to modify this file manually, as it is automatically updated based on the selections made from the relevant windows in GAP.

2.3.1.10 Defining the Working Directory In this option the location of the working directories can be defined:

Whenever a file is open, closed or created, the program automatically selects the files or saves to the data directory defined in these menus. It is recommended to keep data files separate from other program files in a related sub-directory (e.g.: C:\PROJECT\GAPDATA). MBAL executable needs to be defined if reservoir tanks are modelled with MBAL. PROSPER executable location is needed since PROSPER is used to generate well IPR and VLP curves for well models in GAP or used in the PROSPER on line mode. NEW!!! Application startup timeout time can be entered, after which the program will flag that the MBAL and PROSPER licenses cannot be found.

2.3.1.11 Printing from GAP Printer Set Up This will prompt the standard Windows Printer Set-Up window. Use this to GAP User Guide

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select the preferred printing device To print out a current network drawing, select Print from under the File menu. It is possible to print to a hardcopy device, to the clipboard, or to a windows metafile (.WMF). There are options to print in colour, monochrome, or greyscale. The current menu options are: Hard Copy ( the currently selected printer/plotter). Clipboard for subsequent pasting into a word processor or painting package (press to paste the picture). Windows MetaFile for subsequent use in a drawing package For each option the colour choices are monochrome grey scale colour

2.3.1.12 Exiting GAP To exit from GAP, the File | Exit command can be selected. If the file has not already been saved, the program will prompt a screen allowing the user to save the current file.

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2.3.2 Project Archiving When storing or sending GAP files, this option offers the capability of creating an Archive of the whole project. It is in a sense a ZIP file that includes all the associated files required when running the model.

2.3.2.1 Archive Creation To create an Archive, the File | Archive | Create option needs to be selected.

The user will be asked to select a file name for the archive from a file browser: the default extension for GAP archives is .GAR.

Once entered the file name and saved, the User will be presented with a Project Creation screen with the following options:

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Main features The screen contains the following features: Project

Baggage

Project Comment Add Assoc

This is a hierarchical listing of all the files in the project, as also seen from the Edit Project menu option. Select the files that to archive in this list: by default, all valid file paths are highlighted. To select all files, click on the All button. It is possible to double-click on an item in the project list or the baggage list (below) to obtain the basic properties of the file in question It is possible to Add other files that are not directly associated with the project to the archive (for example, Excel spreadsheets or Word documents). To add a file to the archive baggage, type in the file path in the Baggage File field below the Baggage listing (or browse to it using the file browser provided), and press the Add button. The file will then appear in the list box. Duplicate file names are added to the archive only once This field can be used to enter comments describing the project. This will appear whenever one wants to extract the files from the archive, and can help recall the contents of a particular archive. Select the “Write” button to create the .GAR file This adds associated files to the baggage list. For example, if one clicks on a .vlp file in the project list and then click on Add Assoc, GAP will look in the 1990-2011 Petroleum Experts Limited

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same directory as the .vlp file and, if they are present, also add the .tpd and/ or .mbv files to the baggage list. Multiple selections in the project list are possible. The following gives the associated file types for project file types: Well model files (.out, .sin, .anl) Lift curves (.vlp, .tpd, .mbv lift curve import formats) Tank model files (.mbi.mbr (results file)) Action Buttons All/None Add Remove Write

Selects all/no valid files in the project listing Adds a file to the baggage list Deletes the currently highlighted file(s) in the baggage list from the project archive Creates the archive

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2.3.2.2 Archive Extraction To extract the files from an existing archive (*.GAR file), the File | Archive | Extract option needs to be selected from the main menu.

The file can then be selected:

and then GAP will enter the archive extraction screen as follows:

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Main features The screen contains the following features: Project Listing

This is a listing of all the files that comprise the original GAP project. All files are selected by default. Those files that were in the project but the archiver chose not to include in the archive are displayed in light grey. It is possible to double-click on a file to obtain its basic properties. Select from the list those files that to extract: click All Project to highlight all the available files. All files are selected by default Baggage This lists the baggage files that the user chose to add when the archive was created. As with the project listing, the User may double-click on an item to view Listing its properties. Select the file to extract: by default all are highlighted. To select all the files, click on All Baggage Extract Browse to the directory to which one would like to extract the archive files. If the user wants to keep the original directory structure of the archive within the extraction directory, click on Retain Directory Structure and new directories will be created if necessary Comment This displays the comment that was supplied with the original archive GAP User Guide

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Action Buttons All Project Selects all files in the project listing All Baggage Selects all files in the baggage listing Extract Extracts archive files to the directory supplied

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2.3.3 The Options Menu In the following sections, discuss those menu options found under the Options item of the main menu:

2.3.3.1 Method This section allows setting up overall system parameters, including the type of system (production or injection), the prediction mode, and various options on the optimisation process.

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This section defines the type of network that can be modeled in GAP. Production Water Injection Gas Injection Gas Lift Injection NEW!!!

Production systems can contain oil wells (e.g. naturally flowing, gas lifted or ESP wells), gas, or condensate wells The injection manifold takes the place of the production separator at the top level of the system This defines the model as a gas injection network, with the injection manifold taking the place of the production separator at the top level of the system This allows to model the gas lift injection distribution network in detail and to link the gas lift injection network to the main production network model

OPTIMISATION METHOD: This section defines the objective function used by GAP to optimise the system. Production

Revenue

This option optimises the production rate of the primary fluid (in an oil system this is the oil for example). GAP will calculate the maximum rate that can be achieved while honouring production constraints This option optimises on the revenue generated by sales of oil and gas produced after taking into account the cost of processing water and injecting gas. If this option is selected, then prices need to be defined for each fluid in the system (see below). The currency can be defined by selecting "Currency Setup". The following additional data is required to be entered in |Options |Tax Regimes: Revenue from oil sales Revenue from gas sales Cost of water processing Cost of injection gas Cost of power Cost of steam

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Up to 32 different Tax Regimes can be set. The Tax Regime to be used by the system during optimisation can be selected in any well summary screen. The default Tax Regime is selected in |Options |Default Settings. Oil rate only / Those methods are used when the objective is to maximize only the Oil rate, the Gas Rate or the Water rate Water rate only Gas + Oil This method allows to maximise at the same time oil and gas production rate rate only rates and honour constraints Gross This option maximises the gross heating value produced by the field. This Heating Value option is mainly used in the case of gas fields where one would like to maximise the gas heating value of the delivered gas. If the GAP model contains various streams of gas that will contain different compositions and hence gravities, the optimizer will control the system in order to provide at the delivery point a blend of gas that can have the highest possible heating value. In black oil mode, the program will use a correlation to associate the heating value to the gravity of the gas (Figure 4.82 in the Handbook of Natural Gas Engineering published by McGraw-Hill). PREDICTION This option needs to be on “ON” so that GAP can allow the user to carry out a prediction. PVT MODEL This option menu allows to define which PVT model to adopt for the system.

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Four options are available: Black oil Tracking

Black oil model is used for the calculation This method is based on a combination of black oil model and full compositional model (equation of state or EOS): Black oil model is used for the main pressure drop calculations The EOS is then used as a post calculation to determine the composition in any part of the system by performing compositional blends and flashes whenever necessary. If a black oil reservoir simulator (like for example MBAL), the compositional tracking provides with the unique capability to recombined one initial composition in order to match the GOR of the fluid produced Fully This method allows to run all the calculations using an equation of state, Compositional which gives the compositions as well as the fluid PVT properties in any point of the network. NEW!!! This option allows also to perform Lumping/Delumping of an initial EOS, which empowers the user with the possibility to decide if running the calculations using an extended composition, or a using a composition with a reduced number of components (lumped) Black Oil To speed-up calculations, the Black Oil Lumping/Delumping method tracks Compositional the composition of the fluids throughout the network at each iteration of the solver, but performs pipeline, compressor, pump, choke, ... calculations Lumping/ using the Black Oil PVT correlations based on the black oil standard Delumping condition properties calculated by the equation of state. This options makes NEW!!! sure that the black oil model is at any point in time consistent with the EOS. Black Oil Lumping/Delumping may use the full or the lumped compositions Details about the PVT model options can be found further in the manual ( view).

click here 124 to

Note on the EOS: The EOS as models are not predictive, unless matched to measured lab data. Care has to be taken in order to make sure that the EOS has been matched and is applicable for the range of Pressures and Temperatures to be investigated. Black Oil Compositional Lumping/Delumping is the recommended option whenever one wants to speed up the calculations, but still keep them accurate and at the same time provide a consistent composition IMPORTANT NOTE: When modeling gas lifted systems (or any artificial lift systems where a hydrocarbon fluid is mixed to the main fluid) in compositional mode, it is strongly recommended to use the compositional Tracking mode. This is because when using Fully Compositional or Black Oil Compositional modes, a full 1990-2011 Petroleum Experts Limited

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Equation of State model is used to determine the fluid composition and PVT properties. The assumption the EOS model takes is that if two fluids are blended, immediate and perfect mixing occurs and a new fluid is generated. This means that after the mixing it is not possible to physically differentiate between the gas lift gas and the reservoir fluid and separate the gas lift gas from the reservoir fluid, hence it is not possible to have a consistent reporting of the gas lift injected throughout the network, nor to use the gas lift gas rate as a constraint. Compositional Tracking is recommended for gas lifted systems, as it is based on the black oil assumption that the various phases are kept separate throughout the system, hence it is possible to determine and report consistently the amount of gas lift gas at any point in the system and use it for constraint purpose. The black oil assumption behind the Tracking model, though considering separation of the various phases, has been found to be quite reliable, also related to the physical fact that at the relatively low pressure and temperature conditions occurring in pipeline networks mixing of fluids becomes possibly unlikely. Prediction Method This option defines whether temperature calculations in pipelines are performed or not Pressure Only Pressure and Temperature

Temperature changes along the flow lines are not calculated but instead fixed by the user (recommended) GAP calculates both the pressure and temperature losses along the flow lines, using either a simple temperature model or the more advanced Enthalpy Balance option available through the PROSPER on Line option in the pipe description

Wax or Hydrate Warning This option can be used to predict the presence of Wax or Hydrates at any point in the system. The Wax or Hydrate Warning is only available when the compositional details of the fluid are available i.e. when the Compositional Model is set to 'Tracking' or 'Fully Compositional'. By switching this option to ON, if GAP encounters a wax or hydrate risk in the model, it will raise a flag to this effect.

WATER VAPOUR (NEW!!!) This option allows to enable/disable the calculation of condensed water vapour in pipelines. No Water is accounted for as liquid phase by default, unless the pipelines are Calculations modeled with PROSPER on line and the Calculate Condensed Water vapour is enabled in the PROSPER on line options Calculate This option allows to account for vaporization/condensation of water with

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Condensed changing pressure and temperature conditions along the pipelines Water Vapour TEMPERATURE MODEL: (NEW!!!) In previous versions of GAP rigorous temperature modeling with Enthalpy Balance or Improved Approximation could be achieved by modeling the pipelines with PROSPER on line option. Advanced temperature model can now be enabled and used along with the default pipeline modeling option GAP Internal Correlations. Rough This is a heat balance model that calculates the heat loss from the well to the Approximation surroundings based on an overall heat transfer coefficient, the temperature difference between the fluids and the surroundings and the average heat capacity of the well fluids. The Rough Approximation temperature model requires calibration using measured temperature data. It is not accurate in a predictive mode Improved This is a rigorous thermodynamic model that is based on a full enthalpy Approximation balance model considering all the components of energy (enthalpy, potential energy, kinetic energy and heat transfer between fluid and surroundings). The term of the enthalpy balance concerning the heat exchange with the surroundings is simplified by a heat loss term characterized by an overall heat exchange coefficient. For this reason data related to the completion hardware and thermal properties are not necessary. As an enthalpy balance model, Joule-Thomson Effect is also accounted for. These characteristics make this model particularly useful when an accurate calculation of temperature is sought after and only a few data on the completion are available. The Improved Approximation temperature model requires calibration using measured temperature data CALCULATE WELL CHOKE DELTA_T A choke can be placed on the well directly, rather than to explicitly define a choke in the system. By having this option set to YES, GAP will calculate the temperature drop in the fluid as it flows through that choke. If set to NO, temperature drop is not accounted for. BACKGROUND BITMAP The user has the option of adding a picture on the background of the GAP model. This could be a map of the area or an aerial photograph so that the position of the icons on the screen coincides with their real geographical position. Simply select the path pointing to a *.bmp file and this will appear in the main screen as soon as "OK" is selected.

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ASSOCIATED INJECTION MODELS If along with the production network system there are a gas injection and/or a water injection and/or a gas lift injeciton network, it is possible to link them to the main production model by means of this option. The associated injection model(s) for the field can be specified here. Select the check box to indicate that an associated injection model exists, then specify the model file using the button. If no associated injection model exists, GAP will still calculate the injection volumes necessary for the desired injection policy, but will simply assume that these volumes can be injected (not taking into account how they will be injected).

2.3.3.2 Edit Injection Fluids In case the system consists of Gas-lifted wells, Gas Injectors, Water injectors or sources, the properties of the injection fluids need to be defined. The list of injection fluids can be edited from the Options | Injection Fluids screen shown below:

For each source: Enter a unique label. The source Type (Gas, Water, Oil, Steam, Other, Polymer) The source type can be Steam, in which case the default quality need to be entered in this table. The quality is recalculated wherever steam is present in the system, to make GAP User Guide

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sure it is consistent with the steam thermodynamics. GAP uses the Steam Calculation Module from PVTP The source PVT properties Gas gravity and the impurity levels (in terms of mole percentage for the gas). Water salinity for water sources. GOR, API, gas gravity, water salinity and water cut for oil sources If GAP is run using the compositional options, the composition for each source needs to be defined by clicking on the Edit button (the Edit button will only be visible if the composition tracking is chosen). When a new file is created, the list will contain two default items Gas source – Gas01. Water source – Water01 Note about Gas Lifted Wells When gas lifted wells are created, they will (by default) be assumed to be using gas from the first source (Gas01) in the list. The user can change the gas associated with gas lifted wells to another gas source in the list (explained in Gas Lift Control topic 204 ). Note that when a GAP Generate | VLP is performed, the values of the lift gas properties used by PROSPER to generate the lift curves for each well will be taken from the properties of the gas source associated with the well in GAP. The gas lift source data in GAP takes precedence over the current value gas lift gas properties in PROSPER file. The original PROSPER files are changed by GAP, when generating VLP data and gas lift properties section of PROSPER is updated. 2.3.3.3 Edit Tax Regimes When the Optimisation method is set to “Revenue”, the user can define different tax regimes so that different value can be assigned to different fluids in the system.

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Each well in the system can then be assigned either the same or different tax regimes, thus letting the program know the value of e.g. oil coming out of one well as opposed to oil coming from another. The optimiser will then calculate the maximum amount of revenue that can be achieved by the system. The Gas Sales Revenue per BTU switch at the bottom of the screen enables to choose the units in which the gas sales price is described. Cost of steam is part of the variables. 2.3.3.4 Edit Emulsion Models Allows the user to setup and match to measured data different emulsion models to be used to model emulsion behaviour in the GAP network.

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GAP can model the effect of Oil/Water emulsions on mixture viscosity. The behaviour of emulsions in producing equipment is not well understood. Emulsion PVT in GAP provides a means to assess possible effects of increased emulsion viscosity by curve fitting experimentally determined data. It must be emphasised that the method is empirical and does not represent any rigorous model of emulsion behaviour. In the laboratory, stable emulsions can be prepared from many crude oil / water systems. Field experience shows that the effect of emulsions is usually less than predicted by laboratory tests. Emulsion PVT should be used with caution and only when it is certain that emulsions are present and it is necessary to evaluate their effect on calculated pressures. Emulsion viscosity will replace the mixture viscosity for selected elements of the production system. Experimental or empirical emulsion viscosity data can be entered and curve-fitted using non-linear regression. The fitted curve is used to optionally replace the oil/water mixture viscosity in pressure drop and pump calculations. When selected, emulsion viscosity for the user-entered value of water cut will be substituted for the fluid mixture viscosity. Emulsion viscosity is modelled as a function of water cut in 3 stages: Sharp increase at low water cut

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Plateau with a constant maximum viscosity for intermediate water cuts ‘Tail’ that declines to the viscosity of water after the plateau The parameters Left and Right Water Cut for Maximum Viscosity define the maximum plateau region. To calculate emulsion viscosity: - Enter pairs of water cut and emulsion viscosity data points in the Emulsion Data table. - Click the Match button.

When the regression has stopped, click Plot to display the matched mixture viscosity.

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2.3.3.5 Edit Default Settings Allows the user to set the default settings for: Injection Fluids Emulsion Model Tax Regime PVT correlations for pipeline calculations Volume Correction Factors Pipe Line These can be also changed later for each well, source, pipeline, etc. in the model, allowing to use different selections (for example, PVT correlations) in different areas of the system, to reflect the actual situation in the field.

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Default PVT Correlation Volume Correction Factors

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This is the default choice for the water injection and gas injection. Edit Fluid List allows to modify the list of fluids used in the model This is the default choice for the emulsion model. Edit Emulsions allows to modify the list of emulsion models used in the model This is the default choice for the Tax Regimes. Edit Tax Regimes allows to modify the list of Tax Regimes that can be used in the various wells in the system This is the default choice for the Oil Pb, Rs, Bo correlation, the Oil Viscosity and the Gas Viscosity (NEW!!!) correlations When GAP is reporting production rates it calculates Bo and Bg using its own PVT calculator and a ‘virtual process’ occurring at the separator. When interfacing GAP with a process simulator one may wish to apply a correction to the Bo and Bg calculated by GAP to match that calculated by the simulator, which may be using an Equation of State rather than a black oil model. In the fields provided in this screen, one can enter the correction factors to Bo and Bg. Note that these are corrections to the volume ratios, and not the volume ratios themselves. GAP will perform the calculation based on the new values of Bo and Bg This field represents the defaults used when creating a new pipe Default pipe This is the default roughness that will appear as soon as a pipeline element is created. As mentioned above, if roughness required, each pipeline segment can have its own roughness value to represent the actual field configuration Gas/Liquid This cut-off parameter specifies the GOR at which the fluid definition will switch from a liquid to a gas. This triggers the pipe GOR condensate to be treated as an equivalent gas in the Cutoff pipelines as opposed to a liquid. It is recommended to keep this value at default. One can also select the correlation for viscosity based on the one that matches the fluid in the system Water vapour This parameter specifies the value of the GOR above which the water vapour calculations are performed. GOR Cutoff Below the cutoff water is considered to be in liquid phase, (NEW!!!) whilst above the cutoff presence of vapourized water is accounted for. This option is enabled when the water vapour calculations are enabled in the main program Options 74

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2.3.3.6 Edit System Summary This option is used to enter the GAP title and some comments. Title and comments can be displayed on the GAP network, by selecting "Draw Network Title" and "Draw Network Comments" from the View Menu. The Title and Comments can be moved all over the network window, by simply dragging them while the "Shift" key is pressed:

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2.3.3.7 View System Statistics This option allows to visualize a summary of the GAP model, containing the option selected and the number of equipment per type:

2.3.3.8 Disable Options These options switch on/off network data and interface validation. Disable Automatic Masking Disable System

When selecting this option, the Automatic Masking is disabled. This means that if a well is disabled/masked, the pipe downstream the well will not be greyed out, but will appear on the screen in full colour Before accessing any calculation area, the program validates if there are 1990-2011 Petroleum Experts Limited

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Validation

missing/invalid items in the network and will activate a flag highlighting the invalid item. This option disables that validation flag Disable Label The program sets a flag on any item that has an invalid label (for example, two wells with the same name). This option disables that validation flag flag Validation Disable This option (when enabled) allows identifying any inconsistency between the PROSPER/GAP GAP well model type [Oil producer (ESP lifted) for instance] and the well Well Type definition of the PROSPER file associated. In case of inconsistency, the well Validation turns "invalid"

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2.3.4 The View Menu The options under the view menu govern the appearance of the network drawing and activate some validation checks on the individual equipment on the drawing. These can be activated or de-activated as described below:

These options allow to view or not connection lines, masked items, equipment labels, the grid, etc. One important point the users are urged to consider is to leave the system validation options switched on at all times. These will highlight areas at which the model can be improved or corrected. The View menu is divided in these fields: Draw Options 88 Highlight Options 88 Window Aspect and Drawing Options Network Drawing Position 95

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2.3.4.1 Draw Options A series of options are available to modify the view of the GAP network model. The options allow to toggle on/off the visualisation of solid and dotted line connections, tanktank connections, IPR icons, groups and group connections, labels, grid, etc. 2.3.4.2 Highlight Options These options enable/disable the visualisation of specific flags that are usually displayed by the program in the main screen as result of a check of the model status or as a result of a Solve Network calculation. The options available enable/disable: Invalid items (usually highlighted by a thick red circle) Bottle necked pipes (highlighted by a purple colour) TVD differences (see below 88 ) Solver pressure and mass imbalances and Limiting and violated constraints (see below 91 ). 2.3.4.2.1 Highlight TVD Differences This option is used to "highlight" any inconsistence in the pipelines' TVD. An orange circle is displayed around the node where a TVD inconsistency arises. For instance, considering the system below, one can see a TVD inconsistency highlighted on the node "Riserbase":

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Indeed: the TVD of the most downstream point of the pipeline situated upstream of the node "Riserbase" is 0m. the TVD of the most upstream point of the pipeline situated downstream of the node "Riserbase" is 100m.

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Those discrepancies will lead to erroneous pressure drop calculations across the pipelines.

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2.3.4.2.2 Highlight Violated and Limiting Constraints The option to Highlight Violated and Limiting constraints allows to visualise directly on the network after the network is solved is a constraint is violated or is the constraint is limiting the production of a particular element: Violated constraint

This flag indicates that at the end of the Solve Network calculation the constraints could not be honoured. When that happens, it is recommended to review both the model and the constraints themselves, in case there is an inconsistency in the system that causes the constraints to be not achievable (infeasible). Limiting constraints

This flag indicates that the piece of equipment (in the case above, a separator) is limiting the production. In other words, the element could produce more, but constraints imposed on the equipment itself limit the production. These flags can be displayed on any type of equipment where constraints have been set up.

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2.3.4.3 Window Aspect and Drawing Options These options allow the User to modify the aspect of the program window and of the network model drawing, in terms of colours, fonts icon sizes, etc. 2.3.4.3.1 Select Info Displayed Use this option to select what information to display on the main GAP network, in along with each icon.

The section is divided in two main fields: Icon Label This is the information that appears in the main screen along with each element. The default setting is each icon's "label only". Select "Liquid Rate" for instance to display the liquid rate results of the last network solver, along with each icon Icon This is the information that is displayed in the small "fly-over" window that is activated when passing the mouse through each element Tooltip 2.3.4.3.2 Select Default Icon Label Position This option defines the position of each icon label with respect to the icon itself.

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Click on the correspondent position and then OK to change the label position. 2.3.4.3.3 Colours From the View | Colours menu item the user may change the colours of the system drawing and the GAP windows.

To change the customised colour, use the RGB scrollbars on the right hand side of the dialogue. Each colour can be varied from a value of 0 (off) to 255 (full on). The Sample field of the dialogue gives the colour that is obtained by mixing the primary colours in the ratio given.

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There is also a choice of colour schemes, gained by toggling the radio boxes at the top of the dialogue, i.e.: Colour Grey scale

allows full selection of any of the (255 x 255 x 255) colours forces the RGB values to be equal, so that only 255 shades of grey are available Monochrome forces the RGB values to be either on or off, giving a choice of two colours (black or white) Select the drawing component whose colour to alter by highlighting it in the list box on the left. Select from the list box on the left-hand side the element that is to be changed. Select an appropriate colour using the colour-mixing palette on the right. To save the current set of colours for future GAP sessions, click on the ‘Save as user default’ button.

2.3.4.3.4 Icon Sizes The sizes of the icons used to represent the equipment in GAP can be changed. Select the Icon Sizes option from the View menu item, or from the menu obtained following a right hand mouse button click in the system window. The following dialog will appear:

The dialog consists of a slider with a data entry field, which contains the current icon size (this defaults to 60 out of an arbitrary 0 – 100 range for a new file). Change the icon sizes by adjusting the slider or entering a new size in the entry field. Check the Automatic Update box to update the system window with the new size when moving the slider. 2.3.4.3.5 Fonts The fonts used in the network drawing may be changed. To do this, select the Fonts option from the View menu item or from the menu obtained following a right hand mouse button click in the system window. This will bring up a font selection dialog. Select the font size and style required and then OK. The new font will be applied to all system drawings. Fonts for the Items' labels, the Network Title and the Comments can be entered. 2.3.4.3.6 Grid A background grid can be implemented in the GAP model. The settings of this grid can be modified using the Grid option of the View menu. GAP User Guide

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The dialog consists of a two sliders with corresponding data entry fields, which contains the horizontal and vertical spacing of the grid lines. Change these spacings by adjusting the sliders or entering a new size in the entry field. The line type and colour used for drawing the grid can be modified as well. Check the Automatic Update box to update the system window with the new grid dimensions when moving the slider. 2.3.4.4 Network Drawing Position These options allow to modify the placement of the icons in the main program window. 2.3.4.4.1 Normalize Equipment Icons Position and Snap to Grid The objective of these options is to modify the aspect of the network. Normalize Equipment Icons Position Snap to Grid

Resets the system of coordinates used by the program. This is particularly useful when merging different models created according to different zoom scales: at the time of merging the models, this option will reset both models to work with the same scale, allowing to place the systems correctly together When the Grid is active (Draw Grid options enabled), this option places each element in the closest grid corner. This feature is useful to create tidy (squared) network drawings

2.3.5 The Edit Menu In this section, the program allows selection and manipulation of various items on the network for operations such as deleting or in the case of wells, generating lift curves. This section will concentrate on the options which are used for important operations to the model.

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These are the options available in the Edit menu: Undo Options 96 Select Options 97 Selected Equipment Options 98 Find Equipment 104 Edit Options 106 Transfer and Import Options 108 Execute OpenServer Command 2.3.5.1 Undo Options These options allow to undo an operation is performed on the network system drawing. Every time the network drawing is modified, the program will record the action taken. These are the options available: Undo This will undo the last operation made Undo All This will undo all the operations done on the network drawing Clear Undo This will clear the list of changes made on the network list Note that the Undo options are available only for actions done on the network drawing and not on the input data entered in the equipment data entry screens or in the various input menus

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2.3.5.2 Select Options These options allow to select items in the GAP network model. The items can be selected one by one or by the same type (all wells, all joints, etc.). The selection options available are: Select All Items Select All

This option allows to select all the equipment in the network model

Dialogue Select

This option opens up a selection window where one can select the items one by one:

This option allows to select all the elements of the same type, like wells, pipes, tanks, etc., as well as all items that have been disabled, masked, bypassed, etc. To select the type of item to select, choose from the sub-menu:

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Unselect All Items

This option unselects all the selected items. The option is active only when there are selected items in the system

Selected items are highlighted by a cyan circle around them, as shown in the figure below:

2.3.5.3 Selected Equipment Options This section of the Edit menu allows to perform operations on multiple selected elements and elements belonging to the same type that have been previously selected. The options available are: Selected Items

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Selected Wells and Inflows Selected Pipes Selected Tanks 2.3.5.3.1 Selected Items This menu allows to perform bulk operations on all the selected pieces of equipment. For example, after selecting a series of valves, it is possible to bypass all of them at once by using this option.

These are the main options: Disable/Enable This option closes/opens an element. The closing action is irreversible, that is to say, even if during the prediction a scheduled event sets to open the element, this will be kept closed Mask/Unmask This option closes/opens an element. The closing action is reversible, that is to say, if during the prediction a scheduled event sets to open the element, this will opened Bypass / This bypass/unbypass option is applied to inline elements (chokes, valves, inline separators, etc.) Un-bypass Remove This option allows to delete an inline element and to re-establish the connection between the upstream of the inline element and the downstream. (NEW!!!) The objective is to eliminate inline elements from the system without having to re-draw all the connections again. This is the effect of Remove: Initially an inline element is present in the system (in this case, an inline choke):

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After selecting the element with the selection tool Selected Items/Remove, this is the effect:

applying the Edit/

The inline element has been removed and the connection between the well and the pipeline joint created. Show Gradient This option allows to plot the pressure gradient along all the selected pipelines Copy/Cut/ Options to duplicate, cut and delete selected items Delete Extract to GAP This option allows to create a copy of the network or part of it, which can then imported in another GAP project (see below 113 for further details) Partial File (. gpp) Snap to Grid This option snaps the selected elements to grid (see above 95 ) Change Icon This option changes the elements' icon label position Label Position

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2.3.5.3.2 Selected Wells and Inflows This option can be used to perform specific tasks on well icons, for example, setting well head chokes for optimisation:

Set dP Control

This option allow to set the wellhead choke to None (choke switched off), Fixed pressure drop or Calculated (choke set by the optimiser to maximise production and honor constraints) Set Casing Pressure This option allows to switch the Casing pressure control to a fixed value or controlled by the optimiser Control Set Use Casing This option is to switch on/off the casing pressure option Pressure Set Well model This option allows to change the well modeling for the selected wells to: VLP/IPR Intersection, PC Interpolation, Outflow Only - VLP and Outflow only - PROSPER on line. Refer to the Well description 157 for further details Set IPR Rate model This option allows to specify if the IPR is defined in terms of volumetric flow rates of mass flow rates Set IPR Use OriginalWhen running calculations in compositional mode the original composition entered in the model may be changed based on the Composition 1990-2011 Petroleum Experts Limited

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input from the reservoir model (for example when the produced GOR changes as the reservoir pressure decreases below the bubble point). The new composition is called "Working". This option will reset the IPR composition to be the original one initially entered in the model When Composition This option is enabled when one of the compositional models is in use, as well as the lumping/Delumping option enabled. Changes The options available are: Do Nothing (if the composition changes, then use the composition coming from the upstream reservoir simulator as such), Lump (lump the composition of from the simulator) and Delump (delump the composition from the simulator) Refit PC curves This option regenerates the selected wells' performance curves Reset dP chokes This option resets the values of the fixed dP choke applied to the selected wells. Note that the fixed dP choke is the one used when running with no optimisation or with optimisation when Fixed dP Control is selected Turn off if unstable The well outflow features are described in the VLP input section 189 . Allow left hand VLP/ The options here have the objective to switch on/off these features IPR intersection Enable Safe VLP/IPR intersection mode Convert to inflow This option converts the selected wells to inflows eliminating de facto the well outflow from the model Split into This option converts the selected wells into its components inflow and outflow. The application of this feature is in the modeling of inflow and outflow complex well geometries (see example on Smart wells 743 ) 2.3.5.3.3 Selected Pipes This menu allows to change the description of the selected pipes by means of these options:

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Toggle Description Pipe Model

Pipe It switches the direction of the pipe, in case the pipe was incorrectly defined This allows to change the mode used to calculate the pipeline dP ( GAP Internal Correlations, Lift Curves, PROSPER Online) Lumping Calculation In Lumping/Delumping mode (one of the compositional PVT options has to be selected in Options/Method), this option allows to decide if Model. NEW!!! running the dP calculation using the lumped or the full composition Convert to PROSPER This option converts the pipeline (initially modelled as GAP Internal Online Correlations) to PROSPER Online 2.3.5.3.4 Selected Tanks When a prediction has been performed using MBAL tank models or external simulation models, it is possible to switch them to decline curves. The Selected Tanks will allow to import in the decline curve tanks from the production obtained in the initial run by the pre-existing tank model, or from the production obtained by the inflow elements linked to the tank itself.

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2.3.5.3.5 Selected Groups (NEW!!!) Show members as selected This feature allows to highlight as selected all the elements that belong to the selected groups. After selecting the group:

and choosing the Show members as selected option the elements that are part of the group are selected:

2.3.5.4 Find Equipment on System Window In large systems made up of with hundreds of elements, it may sometimes be difficult locating individual items in the drawing, especially in big models where the icons are close together and whose labels are therefore difficult to read. This option pinpoints the location of an item for the user. The top list in the dialog gives the different equipment types available as GAP nodes. When the dialog is invoked, all equipment types are selected. The lower list displays all the system equipment of the selected types, sorted by equipment type and alphabetically. To locate a GAP User Guide

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piece of equipment on the system window, double-click on an entry in the lower list (or select a piece of equipment and then press Locate). A pink rectangle will appear around the icon representing the node in all system views. The rectangle will disappear when leaving the screen.

In the above screenshot, the Separator element called “Separator” will be located on the network by selecting Locate as shown. The requested item will then be highlighted on the main window and on the navigator window if selected. Note that whenever a selection is made in the 'equipment type' list, the list of equipment in the lower list changes to reflect the new selection. Action Buttons All Invert None Locate Edit Select OK

Selects all the equipment types in the upper list Inverts the selection of the upper list Un-selects all the items Locates the currently selected piece of equipment in the system views (equivalent to double-clicking on an item) This invokes the Data Entry screen for the currently selected piece of equipment This selected the highlighted item Clears the screen

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2.3.5.5 Edit Options This sub-menu allows to modify the equipment control set up (for example chokes, gas lift allocation, etc.) and to modify the paths of the files connected by the GAP model. 2.3.5.5.1 Edit Equipment Controls This option has been added in GAP so that users can easily access all the control mechanisms available in the model. In this manner well head chokes, gas lift injection rates, pump power and frequency can be set (prior to a calculation) or viewed (following a calculation) from the same screen:

As an example, consider a situation that the performance of a gas-lifted model needs to be compared to reality. Then the same gas lift injection rates as were injected in reality need to be specified in the model. These can be set from the “Equipment Controls” screen directly as shown above. GAP will then use these injection rates during the unoptimized solve network calculation. GAP User Guide

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The “Edit” buttons will lead directly to the Control page of the individual well models. This can be used to set minimum and maximum constraints for instance. The “Display” and “Control Type” buttons enable to filter the wells to display depending on the control parameter considered or the status of the optimiser for these wells. A specific layout setup can be kept in memory using the “Save Layout as” button. 2.3.5.5.2 Edit Project Paths This option allows all items and associated files in a GAP project to be viewed on a single screen and shows the directory location of the associated files to the GAP network. The paths of the files can be adjusted if required.

This option is useful when having copied a GAP file from one machine to another and the associated file paths are no longer valid. Selecting “All” and “Alter Paths” can allow the user to define the new directory where the associated PROSPER, MBAL etc. files now reside. A typical GAP project is displayed in the example above. The production system file is displayed at the top with any associated well or tank files. Injection system files are listed in a similar fashion below this. If a prediction history file is present this will be displayed at the 1990-2011 Petroleum Experts Limited

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bottom. The list icons are colour coded by type; for example well files are represented by a green icon, tank files by a yellow icon. In addition, a tick or a cross indicates whether the file is a valid file of the required type. From this screen the user may view or alter the properties of associated files, or change the paths of a group of files. Action Buttons Alter Paths

View Details

OK Cancel Apply

Help Select

This is used to change the paths for a group of files. The files to be altered can be selected with the mouse or the Select button as described below. When this button is invoked, a directory browser appears. Navigate to the new directory and press OK. The file list will be updated accordingly This is only active when a single selection is made in the file list. When invoked the File Properties screen appears, allowing the viewing of the file properties or the changing of the file path. The same action is obtained by double-clicking the left hand mouse button on a file list entry Clears the dialog, saving any changes Clears the dialog, ignoring any changes This saves any changes without clearing the dialog. This is useful if an injection file name has changed: this will load the new file and display its contents in the list Invokes this screen Multiple selections from the file list can be made in the usual ways with the mouse. Alternatively, all items might select of a particular type using this button. Choose from the drop-down list the category of file to select. The following choices are possible: All well files All tank files All item model files (tanks and wells) Injection system files (associated gas/water injection systems) Prediction history file When Select is pressed the files of the given type will be highlighted

2.3.5.6 Transfer and Import Options This submenu allows to import in GAP information from various sources, like MBAL Material Balance data, compositional data, gas lift injection input data, etc. 2.3.5.6.1 Transfer Well Data from MBAL Models This screen is used to transfer well data from an established material balance file within MBAL to this GAP model. GAP User Guide

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Various categories of data can be transferred as detailed below. On this screen two lists are shown: on the left is a listing of the components (tanks and wells) of the MBAL model, on the right are the wells of the GAP model. Valid layers are displayed in the GAP well list; transfers to invalid layers can be accomplished by transferring the required data to the well icon itself and then specifying the layer number in the resulting query screen. To transfer data, click on an item in the MBAL list and a destination in the GAP list. Click on a button in the middle to transfer data of the required type. The actual data transferred will depend on the type of the item selected in the MBAL list (for example, tank IPR data will include the tank starting pressure and PVT data, whereas well IPR data includes the PI). In addition, it is not possible to transfer, for example, VLP data from an MBAL tank. Action Buttons IPR

VLP Rel Perm

New Model File

This transfers IPR data from the MBAL item to the GAP target. The data transferred is as follows: From a tank: Starting pressure, Starting temperature, Impurity data (% H2S, water salinity), Gas gravity, Oil/condensate gravity, GOR/CGR. From a well: PI (Darcy coefficients, C and n), Layer type, PI Relative permeability correction (oil layers only), Perforation depths, Breakthrough constraints, Match data, Test water cut / layer pressure Transfers lift curve data to the well in question. This is only possible if the data has been imported into the MBAL well model Transfers either the tank or the well relative permeability depending on the source type. If the MBAL well model is set to 'Use Tank Rel Perm', then this will return the tank relative permeability anyway This will load in an additional MBAL model file (extension .mbi) and display the contents in the list. Choose the required file from the file selection box displayed. Data can then be transferred from the new elements as above.

Note that new files are not stored when the screen is cleared and must be reloaded when going into the screen on subsequent occasions.

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2.3.5.6.2 Initialise IPRs from Tank Simulations This option is particularly useful when history matching a full GAP model. The IPR screens of wells can be initialised with reservoir pressure data and saturations from associated MBAL models at any point of the historical period. This allows checking production from the system at particular points in time rather than running the whole model for the full historical period. It is important to notice that when using this feature, an MBAL simulation will be run up to the initialisation date. The fluid saturations in the reservoir at this point in time will be used along with the set of relative permeabilities defined in the MBAL model in order to obtain the WC/ GOR or WGR/CGR corresponding to this specific date. As with the previous option, more details are provided in the History Matching chapter 510 which deals specifically with History Matching. This screen allows to initialise a well IPR from a tank model (decline curve or material balance). When one invokes the Edit | Initialise IPRs from Tanks menu item, a list of wells appears; select the wells that to initialise and press OK. The list of tanks that are connected to the selected wells appear in a list in the Tank Name column. In order to evaluate the tank pressure and PVT the tank models must have a history in the case of MBAL models or, in the case of decline curve models, production data. These are the options available: MBAL Start Date MBAL End Date Start Cumulative Production Pressure Start Date

For MBAL models only - the start date of the tank history For MBAL models only - the end date of the tank history For Decline Curve models - the cumulative production at which the pressure and PVT data are to be evaluated Displays the pressure following a Calculate For all MBAL tanks, this is the date at which the pressure and PVT should be evaluated

Action Buttons Calculate Continue Cancel

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Evaluates the tank pressure and PVT at the specified date/cumulative production, and displays this in the Pressure column Calculates the PVT and pressure data at the required conditions, and places this in the IPR data of those wells that were selected initially Clears the screen, ignoring any changes

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2.3.5.6.3 Import Compositions NEW!!! This option allows to automatize the import of Equation of State (EOS) in GAP. When the model is in compositional mode, the Import Compositions feature allows to import in one go EOS for multiple wells. Select from the list of wells the wells to import the EOS for:

Two selection boxes are available to import the Lumping Rules - in case Lumping/Delumping is activated in the main program options, under EOS Model Set up - and the EOS Options - in case the imported EOS file contains different options that need to be taken into account, like different volume shift set up, different path to standard, etc. Then Continue and recall the .PRP file containing the required EOS: the EOS will be automatically imported in the wells' IPR input section. 2.3.5.6.4 Lump/Delump Compositions NEW!!! This option allows to apply a lumping rule in batch model to multiple wells.

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2.3.5.6.5 Transfer Options for Gas Lift Injection NEW!!! When Gas Lift Injection network model is associated to the Production network model, three options are available: Transfer Well Gas Lift gas rates to Injection System Sinks Transfer Injection System Sink pressures to Gaslifted Wells casing pressure

When a Solve Network calculation (for example, an optimisation) is performed in the Production system, the gas lift rates used by each well can be passed to the Gas Lift Injection system, which can then be used to calculate the pressure required to flow the gas When a Solve Network calculation (for example, an optimisation) is performed in the Gas Lift Injection system, the pressure calculated for each well (casing head pressure) can be passed to the Production system, which can then be used to calculate the production that can be obtained applying those casing pressures

Transfer Production System This option transfers the Production separator pressures Separator pressures to to the GasLift Injeciton Manifolds Gaslift System Injection Manifolds 2.3.5.7 Execute OpenServer Statement This feature allows to perform the basic OpenServer operations on any element of the GAP model. The basic operations are: DoGet DoSet DoCommand

To retrieve values of input data or results To input data in the system To perform actions (like masking items or run calculations)

Examples of applications are: masking multiple elements at the same time, or reading the result of a particular element.

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To use the feature enter the OpenServer string (and the value, if using DoSet to input data in the model) and then select the Mode and then Evaluate to execute the command. In the Returned value and message the program will highlight if the command has been successfully executed. Using the wildcard $ in the place of the equipment label or index will allow to access all the items of the same type in one go. For example: DoCmd("GAP.MOD[{PROD}].WELL[$].MASK()") will mask all the wells in the system. This feature can be used to change in one go parameters like pipe diameters or rest the input of all the elements of the same type. 2.3.5.8 Importing GAP models in an existing project GAP allows to build and match entire production sub-systems independently and to then combine them to Build the overall system model prior to doing the gas allocation. This section explains how to save .GPP files for sub-systems and recall them later to assemble a complete system model. Saving a .GPP File Once a sub-system model is set up (for example a platform in a multi-platform gathering system), select all the items in this model by selecting the menu Edit / Select All Items:

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The model will then be selected (cyan circles will indicate the selected items):

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Note that the section to export can be also selected manually using the cyan arrow selection tool from the button toolbar. This allows to select sections of the system. It is now possible to save the selected section of network as a GAP Partial file (.GPP) by selecting the menu Edit / Selected Items / Extract to GAP partial fil (.GPP):

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and then save the .GPP file:

GAP saves a .GPP file that contains all the data for the system elements below. Recalling a .GPP File In the destination model, it is possible to import the just saved GAP model by right-clicking on the main screen of the GAP model and selecting the option to import the .GPP file:

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This will allow to import the already saved .GPP file into this system and connect it as appropriate:

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In this manner, the entire system can be built up from sub-systems that have been independently prepared and matched.

2.3.6 The Constraints Menu This menu provides access to the constraints applied on the entire system or to the constraints applied on each of the system equipment.

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then be introduced to make selected system elements behave as desired during the optimisation phase. General constraints (as opposed to abandonment constraints) are displayed with two RED arrows pointing towards the element that is constrained. Abandonment constraints are displayed with two BLUE arrows pointing towards the element that is constrained (NEW!!!). 2.3.6.1 System Constraints The GAP system is defined as the total production from all separators. System constraints can be used to model, for example, pipeline export capacity for a platform with several separation trains. GAP constraints are used to direct the Optimiser algorithm and should not be confused with well limits used in prediction runs to shut in high GOR wells (for example). In this screen one can enter the global constraints that apply to the system. These constraints are independent of the constraints that can be applied to each item in the system. To set the total system constraints such as maximum water, gas, liquid and oil throughput, choose “System Constraints”. The following screen appears:

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These parameters are used to define the maximum and minimum production levels for the system, where appropriate. When left blank, the program will assume no constraint for a particular variable. The Unscheduled Production Deferment constraint enables to take into account the effects on the production of any non-scheduled events. The influence of these events will be taken into account statistically as an overall percentage of production. Therefore, if an unscheduled production deferment value of 5% is specified in the system constraints section, the entire field will only produce 95% of the total production calculated by the solver. This deferment is applied to all average and cumulative rates, but not on the instantaneous rates. It is important to notice that this constraint, if used, will overwrite any downtime applied at well level. The excessive use of constraints within GAP is discouraged. Constraints should never be used during the matching phase of the model building process. Once a system model has been successfully validated against actual measured rates, the minimum number of constraints should then be introduced to make selected system elements behave as desired during the optimisation phase. Field Tabs Value Binding (Yes/No)

Potential (Yes/No)

Enter in this screen the value of the constraint to be set in any element of the model Selects which constraints are binding or not. The optimiser will always try to honour all the constraints set in the model, however when constraints are set to binding Yes the optimiser will iterate until the constraints is honoured (provided it is feasible) whilst in the case on NO binding if the constraint can not be achieved (because physically infeasible) it will be neglected Enables to include the constraints in the potential calculation. Those constraints set to NO will not be considered in the Potential calculation

Enter the levels of production for each item. Constraints should not be required in the matching phase of the GAP processing. Action Buttons OK Cancel

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Use this button to produce a report of the data. Reports can be written to a file, the Windows clipboard, the screen, or a hardcopy device. See the Reports menu item for more information Use this button to access this screen

2.3.6.2 Binding (Yes/No) Binding (Yes/No) Selects which constraints are binding or not. The optimiser will always try to honour all the constraints set in the model, however when constraints are set to binding Yes the optimiser will iterate until the constraints is honoured (provided it is feasible) whilst in the case on NO binding if the constraint can not be achieved (because physically infeasible) it will be neglected 2.3.6.3 Edit Constraints Table In GAP it is possible to set constraints on production or injection at every level of the system. This option allows viewing, checking or editing the specific constraints of a group of selected element items in a single edit session. When the option is invoked, a constraints screen will be produced for the first equipment item in the selection list. This screen contains Next and Previous buttons for navigation through the list. For each element, enter the required constraints into the dialog. This option provides a single table from which all the constraints in the system, as well as the system constraints, can be viewed and edited. An example of the dialog produced is as follows:

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The “Type” and “Sub Type” selection menus enable to filter the constraint tables as a function of the type of element considered. There are three screens that allow the user to enter the values for constraints, whether they are binding or not and whether they should be included in the potential calculations or not. When setting a constraint as Binding or Not Binding, the program will in both cases try to honour the constraint, with the difference that in the case of the binding constraint the program will iterate until the constraint is honoured (if it is feasible), whilst in the case of not binding constraint, if this cannot be respected, it will be neglected. In general constraints like maximum rate or also NO-CLOSE Minimum Gas Injection Rate should be set as binding, because in most cases these are feasible and we want the optimiser to try to honour them.

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When any element of the system has been constrained, two arrows pointing towards the element appear. The arrows are red if the constraint is a "General" constraint The arrows are blue if the constraint is a "Abandonment" constraint (NEW!!!) Field Tabs Value Binding (Yes/No)

Potential (Yes/No)

Enter in this screen the value of the constraint to be set in any element of the model Selects which constraints are binding or not. The optimiser will always try to honour all the constraints set in the model, however when constraints are set to binding Yes the optimiser will iterate until the constraints is honoured (provided it is feasible) whilst in the case on NO binding if the constraint can not be achieved (because physically infeasible) it will be neglected Enables to include the constraints in the potential calculation. Those constraints set to NO will not be considered in the Potential calculation

Action Buttons: OK Cancel

Removes the dialogue and saves any changes made Removes the dialogue and ignores any changes made

Help

Displays this screen

2.3.6.4 Edit Abandonment Constraints Table This option allows viewing, checking or editing the specific abandonment constraints of a group of selected element items in a single edit session. (NEW!!!) Abandonment constraints are displayed with two BLUE arrows pointing towards the element that has the constraint.

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2.4 Describing the PVT The following paragraphs summarise the steps to be taken in setting up the PVT options in GAP based on the objectives and amount of PVT information available. Under the system Options/Method four main options are available to model the fluid PVT:

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Black oil Tracking

Black oil model is used for the calculation This method is based on a combination of black oil model and full compositional model (equation of state or EOS): Black oil model is used for the main pressure drop calculations The EOS is then used as a post calculation to determine the composition in any part of the system by performing compositional blends and flashes whenever necessary. If a black oil reservoir simulator (like for example MBAL), the compositional tracking provides with the unique capability to recombined one initial composition in order to match the GOR of the fluid produced Fully This method allows to run all the calculations using an equation of state, which gives the compositions as well as the fluid PVT Compositional properties in any point of the network. NEW!!! This option allows also to perform Lumping/Delumping of an initial EOS, which empowers the user with the possibility to decide if running the calculations using an extended composition, or a using a composition with a reduced number of components (lumped) Black Oil To speed-up calculations, the Black Oil Lumping/Delumping method tracks the composition of the fluids throughout the network at each Compositional iteration of the solver, but performs pipeline, compressor, pump, Lumping/ Delumping NEW!!! choke, ... calculations using the Black Oil PVT correlations based on the black oil standard condition properties calculated by the equation 1990-2011 Petroleum Experts Limited

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of state. This options makes sure that the black oil model is at any point in time consistent with the EOS. Black Oil Lumping/Delumping may use the full or the lumped compositions In the case where Tracking or Fully Compositional or Black Oil Compositional Lumping/ Delumping is selected, as shown below, then an Equation of State will be required to be set up in order to either track the compositions in the system or get the PVT directly from the EOS. This section describes more in detail the various options available in GAP for both black oil and compositional modelling. IMPORTANT NOTE: When modeling gas lifted systems (or any artificial lift systems where a hydrocarbon fluid is mixed to the main fluid) in compositional mode, it is strongly recommended to use the compositional Tracking mode. This is because when using Fully Compositional or Black Oil Compositional Lumping/ Delumping modes, a full Equation of State model is used to determine the fluid composition and PVT properties. The assumption the EOS model takes is that if two fluids are blended, immediate and perfect mixing occurs and a new fluid is generated. This means that after the mixing it is not possible to physically differentiate between the gas lift gas and the reservoir fluid and separate the gas lift gas from the reservoir fluid, hence it is not possible to have a consistent reporting of the gas lift injected throughout the network, nor to use the gas lift gas rate as a constraint. Compositional Tracking is recommended for gas lifted systems, as it is based on the black oil assumption that the various phases are kept separate throughout the system, hence it is possible to determine and report consistently the amount of gas lift gas at any point in the system and use it for constraint purpose. The black oil assumption behind the Tracking model, though considering separation of the various phases, has been found to be quite reliable, also related to the physical fact that at the relatively low pressure and temperature conditions occurring in pipeline networks mixing of fluids becomes possibly unlikely.

2.4.1 Black Oil If the PVT model model is set to “Black Oil” the PVT properties used in the pressure drop calculations will be determined with a Black Oil model. The term “Black Oil” refers to a PVT model that considers the fluid to be (when below saturation conditions) split between a Liquid and a Gas (2 Phases) in equilibrium. The basic implicit assumption is that the liquid and the gas are characterised by a fixed composition, no matter the pressure and temperature conditions. Correlations are used to calculate the Bo, Bubble Point, Gas Oil Ratio etc from measurements at surface (API gravity, gas gravity etc). This definition can be extended to gases and condensates where correlations can be used to get the CGR, dew point

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and other properties. Hence the existence of “Black Oil” PVT models for condensates. In the MBAL and PROSPER parts of the manual, the black oil models have been described in more detail. This description includes: Entry of basic Black Oil PVT data Matching of lab data to correlations Selecting the best correlation Discussion on the use of tables The origin of the black oil properties used by GAP to perform the network calculations depends on the way the model is run: When running the model in Solve Network mode, the black oil properties used by GAP are the ones present in the well IPR input section and that were imported from PROSPER with an IPR generation 390 :

When running the model in Prediction mode, instead, the PVT black oil properties of the fluid produced from each well will be obtained at every time step from the reservoir model (MBAL or an external simulator). The PVT information transferred from PROSPER and present in the IPR screen of the well models in GAP will be overwritten, along with the reservoir pressure and possible PI (if a simulation model is used for instance). GAP will then feed this PVT information to its internal PVT model (defined in Default Settings 82 ), thus being able to calculate all the PVT properties necessary when calculating pressure 1990-2011 Petroleum Experts Limited

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drops in the system. When two or more fluids are present in the system, GAP will mix the fluids at every joint where they meet in order to get the parameters for the fluid that results from the mixing. The gravities, GORs and CGRs of the resulting fluid will be calculated by means of a mass balance (mass of blending fluids = mass of resulting stream). At every joint where different fluids mix, a new fluid model will be generated based on the properties and volumes of the original fluids. This new description will then be used for calculations downstream of this joint.

2.4.2 Compositional Options In GAP three main compositional PVT model options are available, which allow to determine the fluid composition everywhere in the system and its variation with changing reservoir conditions: Tracking Fully Compositional

click here 142 click here 143

Black Oil Compositional Lumping/Delumping

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Details about each PVT model option are reported in the next few sections (click on the above links to access them). IMPORTANT NOTE: When modeling gas lifted systems (or any artificial lift systems where a hydrocarbon fluid is mixed to the main fluid) in compositional mode, it is strongly recommended to use the compositional Tracking mode. This is because when using Fully Compositional or Black Oil Compositional modes, a full Equation of State model is used to determine the fluid composition and PVT properties. The assumption the EOS model takes is that if two fluids are blended, immediate and perfect mixing occurs and a new fluid is generated. This means that after the mixing it is not possible to physically differentiate between the gas lift gas and the reservoir fluid and separate the gas lift gas from the reservoir fluid, hence it is not possible to have a consistent reporting of the gas lift injected throughout the network, nor to use the gas lift gas rate as a constraint. Compositional Tracking is recommended for gas lifted systems, as it is based on the black oil assumption that the various phases are kept separate throughout the system, hence it is possible to determine and report consistently the amount of gas lift gas at any point in the system and use it for constraint purpose. The black oil assumption behind the Tracking model, though considering separation of the various phases, has been found to be quite reliable, also related to the physical fact that at the relatively low pressure and temperature conditions occurring in pipeline GAP User Guide

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networks mixing of fluids becomes possibly unlikely. 2.4.2.1 EoS Model Setup When any of the three compositional options (Fully compositional, Tracking and Black Oil Compositional Lumping/Delumping) is selected, the setup of the model is exactly the same. The main difference among Tracking, Fully Compositional and Black Oil Compositional Lumping/Delumping is the way the EOS model is used (see sections for each option). Results can be viewed in exactly the same way too. Once any of the compositional options have been selected from the System options menu, the EOS Model Setup will be displayed.

This allows to access a configuration section, where the EOS options can be selected:

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These options should reflect the EOS available for the fluid (from PVTP for example) and the process (path) the fluid follows to standard conditions (which will affect the volumes and quality of the resulting fluid). In this section various families of options allow to decide how to run the calculations: General In this field it is possible to decide which EOS model to select, as well as the calculation engines.

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The choice is between the two industry-standard cubic EOS models: Peng-Robinson and Soave-Redlich-Kwong This defines how the calculations are run. Our PVT experts have been working on ways to speed up the calculation of properties from an EOS model. Speed is one of the main issues with fully compositional models and the options in this field will define the speed of calculations. The objective of this option is to speed up the calculations without penalising the accuracy the results. The Medium mode is the fastest (up to 80 times) and also default and this should be selected unless any problems are detected in the calculations When repetitive calculations are performed, this option can be selected to reduce the number of compositional calculations performed (increase of speed by up to 40 times). This option is particularly useful when running with Black Oil Compositional Lumping/Delumping: the determination of the equivalent black oil model is done only when the composition changes. If the composition does not change, that means that the black oil properties remain indeed the same, hence it is not required to use the EOS to re-calculate the black oil properties

Volume Shift In this field it is possible to decide if to apply the Volume Shift correction or not to the EOS. Note that if Lumping/Delumping is enabled, it is possible to enable/disable the Volume Shift in both the full and the lumped compositions:

If no Lumping is enabled, the only Full composition volume shift option is available. Lumping NEW!!! This option allows to enable working with Lumping/Delumping of composition.

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Allow Lumping

If No is selected, no Lumping/Delumping is allowed, which means that each fluid in the system is defined by one EOS composition. Of course the composition can vary depending on the reservoir conditions. This option is selected whenever a Fully Compositional calculation is performed using a unique fluid PVT definition If Yes is selected, the Lumping/Delumping options is enabled, which means that each fluid in the system can be characterised by two equivalent EOS compositions, a full (high number of components) and a lumped (reduced number of components) and the user can decide which one to use for the calculations and to pass from one to the other consistently (ref. Lumping/Delumping 6 )

Mode

This option defines which composition is used in the network calculations Use Full Comp The full composition is used for the calculations Use Lumped Comp The lumped composition is used in the network calculations. This option defines also which composition is run in the MBAL models connected in the case that Lumping/ Delumping is enabled in the MBAL models too

Master Rule

This field allows to select the Master Rule used to perform Lumping/Delumping (ref. Lumping/Delumping 6 ). the Master Rule can be created or imported from PVTP and contains the logic followed to pass from an extended compositon to a lumped one (lumping) and viceversa (delumping). The Master Rule is the logic applied to all the network (included any MBAL model connected)

More Lumping

This section defines the Lumping Rule used in the whole GAP model. See paragraph below 135 for further details

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Reference Data for Standard Conditions This section defines the Reference Standard Temperature and Pressure used to express the flow rates. It is important to remark that this option affects only the standard temperature and pressure used to express the liquid rates. As far as the gas rates are concerned, the standard conditions are by definition defined by the particular Unit System. For example, if the Unit System is Oilfield, the gas rates are expressed in Scf or MMscf (where "S" indicates standard volumes), which are by definition at 60 deg F and 0 psig. Set as Default allows to set the entered conditions as program default. Blending This section defines the rules followed by the program when two or more fluids compositions mix. Match Components

Component Name Only

by Component Name or Properties Use Number of Components as key

The program will mix only the properties of components that have the same name. When suing this option the user has to make sure that the mixing compositions have been defined with the same number of components and same names The program will mix only the properties of components that have the same name or similar properties (Tc, Pc, etc.) If Yes is selected, the program will try and blend components that correspond to the same component number. If components in two blending compositions have different names, these will be blended. If No is selected, if components in two blending compositions have different names, the components will not be blended, but they will be carried on as separate components. The sketch below shows the concept: "No" is selected:

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This option allows to even use compositions with different number of components. If that is so, each new set of pseudo component will be carried along. Phase Check This section allows to decide the method used for the phase detection. This option should not be modified. Path to Surface and Recycle This field defines the path followed by the fluid down to standard conditions. When expressing rates, in fact, they are conventionally defined at standard conditions. However, depending on the path followed, more or less gas/oil can be reported. In general the path to STD used in the model should be consistent with the path used in the field to meter the phase rates. Flash Straight

Means that the fluid is flashed straight to STD

to Stock Tank Use Separator

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down to STD

Use K Values

Option is an addition to the compositional modeling that allows modeling the process based on K values (equilibrium ratios). This can allow process calculations from systems more complex than separation to be represented as “Pseudo” separators and can be obtained from process simulators. Note that the use of K values is discouraged by the fact that they depend on the fluid composiiton: if that changes, the k values may not be representative anymore, therefore incorrect answers may be obtained

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Target GOR Method The objective of the Target GOR is to recombine and original fluid in order to reproduce the produced GOR. In other words the objective is to determine the evolution of the fluid composition as the GOR changes. To achieve that, the program determines a gas and a liquid from the original composition and then it recombines them in order to reproduce the actual producing GOR. This entry option defines the source of oil and gas used to recombine the fluid. Use Separator Fluids Use Fluid from PSAT

The oil and gas come from flashing the fluid through the entered separator train. This option is the default as it works in all cases The oil and gas come from flashing the fluid to a few psi below the saturation pressure. It should be noted that this restricts any target that can be found to the RS of the oil below PSAT and the GOR of the equivalent gas. Although more restricted, this mixture better reflects the case of an oil entraining gas cap gas etc. The limits on the GOR target are displayed as the min and max GOR. A reservoir or layer temperature is required for this method. The PSAT is found at the entered temperature

2.4.2.1.1 More Lumping NEW!!! The More Lumping button allows to access the Lump Option Dialog, where the details of the Lumping Rule are present and can be edited, as well as the Lumping Rule itself can be defined.

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The Lump Options available are: Lump Rules This section allows to select the Master Rule used throughout the GAP model. Lumping Rules This contains a table with the list of lumping Rules imported in the GAP model. Selecting Select it is possible to Import/Export, view or edit the Lumping Rule:

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In the Lumping Rules Summary Dialog section the lumps are described (for example, in the figure above the first lump is N2C1, which is given by the sum of N2 and C1), giving the correspondence between the lumped and the full composition. At the top right of the screen a BIC Multiplier is reported, This is a multiplier to the Bi coefficients of the lumped composition, which is a methodology available to make sure that the lumped composition reproduces the same saturation pressure as the full composition. The Setup button allows to define the logic behind each lump, for example:

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The remaining options are self-explanatory. General This section allow to select the options for Lumping/Delumping. Allow Lumping and Mode are the same as reported in the main EOS Setup section ( above 131 ). As far as the other options are concerned: Seps

Use Full Composition for Enthalpies

see

It is possible to perform Lumping/Delumping using gas and oil obtained by flashing the fluid straight to Stock Tank or through separator stages One of the main reasons why surface and process models need to have a large number of components is that thermal calculations (heat capacities, enthalpies) require a very detailed composition in order to be accurate. This option forces the program to use the full composition every time enthalpies need to be calculated, and should always be selected

DeLumping This section allows to define the techniques used to Delump a lumped composition. DeLump Method

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with the Target GOR method to make sure to reproduce the lumped composition's GOR. This option is default and also recommended This option makes sure that the full composition obtained matched the GOR of the lumped composition Only the Lumping Rule is applied

Use DeLump Rule Only This option makes sure that the C1 amount is preserved when passing from the de-lumped to the lumped composition. This is useful to quality check

Lumping This section allows to define the techniques used to Lump a full composition. Lump Method

This option defines the method to determine the lumped composition from the full. The options are the same as in the DeLump Method options

2.4.2.2 Setting up a Compositional model The process of building a GAP model when any of the compositional options is enabled (PVT model set to Tracking or Fully Compositional or Black Oil Compositional Lumping/Delumping) is always the same. The following steps illustrate how to set up the model to use an EOS: 1. Enable the desired PVT Model from the Options | Method entry screen. 2. Compositions need to be entered at the well level. Note that it is also possible to perform a batch import of compositions by using the menu Edit / Import Compositions ( related topic 111 ). To do it on a well-by-well basis, go to the well data input screen and navigate to the composition tab. In this screen total fluid compositions are entered for the entire well production (single-layer case) or for each valid layer of a multi-layer case. Select the layer for which one wishes to enter a composition (if applicable) and press the Composition button. Compositional information can be entered into the resulting screen by hand, imported from a PROSPER .PRP file, or pasted from a spreadsheet application (e.g. Excel). In this screen one may also perform phase envelope calculations and plotting.

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When the composition has been entered, press OK. The colour of the Composition button on the well composition entry screen will tell if the composition entered is valid. Repeat this for all wells. 3. For gas lifted wells, one must ensure that the gaslight source has an associated composition. This can be determined from the Well Gas lift Input screen: the colour of the composition button will indicate whether there is a valid composition or not. If there GAP User Guide

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is not, access the Gas Injection Source table from this screen and enter a composition from here. 4. (Prediction only). If there is gas voidage replacement / injection, then the composition of this needs to be specified. If there is no associated gas injection system, then the composition of the injected gas can be entered from the Prediction Forecast Set-up screen or from the Tank Injection Entry screen. 5. If there is an associated gas injection system then the injection source has to be specified per injection manifold of the injection system. Go to the gas injection system and enter the injection source from the Injection Manifold Injection Source screen. In either case the injection source must be selected from the list of gas injection sources maintained with the production system. During the prediction run the wells will take the fluid compositions from the tanks, provided these have been set up in the MBAL model. If one reloads a snapshot following a prediction run the well compositions will lbe filled in accordingly. When a reservoir model (MBAL or an external simulator) is linked to GAP, the composition comes from the reservoir model. If the reservoir model is not compositional (for example, black oil), GAP will use the composition entered in the well IPR section and will recombine it in order to match the fluid properties (GOR) coming from the reservoir model. This means that GAP is able to determine the composition even if the reservoir simulator is not. If Lumping/Delumping is selected in the EOS Model Setup options, then at step 2. it is possible to import a .PRP containing both the lumped and the full compositions (see figure below). The Options will then decide which of the two to use for the calculation and where to perform the lumping/ delumping.

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2.4.2.3 Tracking If Tracking is selected as PVT model option, GAP uses the black-oil model in its calculations, and an EOS composition is carried along and used to determine (track) fluid compositions from the well bore through the surface network system and the composition of oil and gas whenever a separation process occurs (for example, before a pump or after a separator) by means of flash calculations. The compositional tracking features allow taking advantage of the speed of the Black Oil calculations and getting the resulting composition of the fluid at every node. Provided that the pressure drops will not be affected significantly by the fact that the EOS is not used directly for the PVT properties, then this method can yield very good results without compromising on speed. In a stand-alone (non-predictive) mode, the compositions are entered at the well level (well IPR input area). In a prediction run (see related chapter 453 ), GAP requires that compositions have been set up in the tank MBAL models. Compositions are tracked during the Solve Network or during one prediction time step process: GAP calculates fluid rates and specific gravities referred to surface conditions throughout the system. From these mass flow rates, and hence mole rates, can be evaluated. Compositions at manifolds are then found by a simple combination of molar quantities of the input stream compositions. GAP User Guide

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By working from the bottom (well) level up, the composition of the fluid at the separator can be deduced If the fluid GOR changes along the time (for example, during a prediction, if the reservoir pressure goes below the bubble point), the program will recombine the initial composition entered in the well IPR section in order to match the fluid GOR. This recombination technique is called Target GOR. Gas injection at wells or in injection systems is handled in the same way. Knockout of gas at joints is achieved by flashing the fluid to the manifold operating pressure and temperature, and then removing the specified number of moles. At the beginning of any calculation GAP will inform of the success of the tracking: the tracking will fail if there are any missing compositions or in the unlikely event of a calculation failing. When running the model as tracking, it is possible to set in the EOS Model Setup options ( see above 129 ) if to run with the composition as it is, or if to perform Lumping/Delumping. This allows to decide if the composition to track is the full or the lumped one. IMPORTANT NOTE: When modeling gas lifted systems (or any artificial lift systems where a hydrocarbon fluid is mixed to the main fluid) in compositional mode, it is strongly recommended to use the compositional Tracking mode. This is because when using Fully Compositional or Black Oil Compositional modes, a full Equation of State model is used to determine the fluid composition and PVT properties. The assumption the EOS model takes is that if two fluids are blended, immediate and perfect mixing occurs and a new fluid is generated. This means that after the mixing it is not possible to physically differentiate between the gas lift gas and the reservoir fluid and separate the gas lift gas from the reservoir fluid, hence it is not possible to have a consistent reporting of the gas lift injected throughout the network, nor to use the gas lift gas rate as a constraint. Compositional Tracking is recommended for gas lifted systems, as it is based on the black oil assumption that the various phases are kept separate throughout the system, hence it is possible to determine and report consistently the amount of gas lift gas at any point in the system and use it for constraint purpose. The black oil assumption behind the Tracking model, though considering separation of the various phases, has been found to be quite reliable, also related to the physical fact that at the relatively low pressure and temperature conditions occurring in pipeline networks mixing of fluids becomes possibly unlikely. 2.4.2.4 Fully Compositional If the PVT model is set to Fully Compositional, GAP will use an EOS model to determine the fluid PVT properties used in the network pressure drop calculations. At each network node the program will perform a full flash calculation using the EOS composition to determine the liquid and vapour in equilibrium and their properties (FVFs, 1990-2011 Petroleum Experts Limited

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densities, viscosities, phase split). When two different fluid streams blend, GAP will perform mass balance (in molar basis) to determine the composition of the resulting fluid. Whenever there is a phase separation (before pumps or compressors, inline separators, main separators, etc.) the flash calculation allows to determine the compositions of oil and gas and the flow rates. When running Fully Compositional, GAP internally works in molar basis. As the rates are conventionally reported in volumetric (at standard conditions) basis, the programs converts every time from molar rates to volumetric rates. The flow rates reported by the program at any point in the network correspond by definition to volumetric rate expressed at Standard Conditions (STD, by default 60 deg F, 0 psig, but these conditions can be modified in the main program Options) and not in in-situ conditions. For example, if oil rate = 500 STB/day, that means: taking the whole fluid to STD, the volume of oil produced resulting is 500 STB/d When running the model as fully compositional, it is possible to set in the EOS Model Setup options ( see above 129 ) if to run with the composition as it is, or if to perform Lumping/Delumping. This means that to run compositional with Lumping/Delumping (NEW!!!) one has to simply switch on the option Lumping.

2.4.2.5 Black Oil Compositional Lumping/Delumping NEW!!! If Black Oil Compositional Lumping/Delumping is selected as PVT model option, GAP uses the black-oil model for its calculations, and an EOS composition is carried along and used to determine (track) fluid compositions from the well bore through the surface network system and the composition of oil and gas whenever a separation process occurs (for example, before a pump or after a separator) by means of flash calculations. The difference with Tracking is that in Tracking the EoS originally entered in the well IPR section is recombined in order to match the black oil GOR and the black oil properties where fixed by the well IPR section (in in Solve Network calculations) or by the reservoir model. In the case of Black Oil Compositional Lumping/Delumping, instead, the EOS is used in a full compositional calculation, however, whenever a pressure drop calculation is performed, the program determines a black oil model from the EOS and uses the black oil model for the calculation. This option ensures that the black oil model is always consistent with the EOS and is in general the recommended option to adopt when accurate results and at the same time quick run times are required.

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The Black Oil Compositional Lumping/Delumping is able to model fluids where the EOS does not give accurate results, like for example heavy oils, where black oil correlations for viscosity are more reliable than the standard LBC correlation used when running composition. When running the model as Black Oil Compositional Lumping/Delumping, it is possible to set in the EOS Model Setup options ( see above 129 ) if to run with the composition as it is, or if to use Lumping/Delumping. This allows to decide if the composition to use along with the black oil is the full or the lumped one. As the model is very fast, the Full Composition can be selected.

2.4.2.6 Viewing Compositional Results Whenever running the model in Tracking or Black Oil Compositional Lumping/Delumping or Fully Compositional, it is possible to view the composition everywhere in the GAP network for any calculation performed. Compositions for all nodes can be viewed from the Solve Network or the Prediction results as required. When inspecting the Solve Network results, the fly-over allows to view the compositional results:

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View / Select Info Displayed. Alternatively, results can be viewed in any of the Results screens. It is also possible to view the full table of composition by going to the results screen of the node in question, scrolling to the right end of the table, and clicking on the View Composition button for the desired result:

The composition data entry screen will be displayed with the composition for that node, at the network-solve / time step investigated. The View Composition screen is common to all the results screens in IPM and allows to: view the composition export the composition (for example for further analysis in PVTP or PROSPER) and have further utilities like Generate (which reproduces a CCE experiment), Phase Envelope, Target GOR (to determine how the composition varies with changing GOR), Properties (straight flash to Standard conditions using the Separator Information

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When Lumping/Delumping is performed, in the View Composition screen it is possible to view one composition or the other by using the View toggle:

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2.5 Equipment Data After completing the system drawing, the unique characteristics of each element must be entered. This and the following chapter describe how to enter data to describe the properties of each of the system elements. In this chapter main equipment data entry / results display screen format is described. This is the place from where all equipment data can be entered and results of calculations for that equipment are stored. This is followed with a detailed description of the input data that is required for a full description of a well model in GAP. Finally, the results screens that apply to all item types will be described.

2.5.1 Introduction This chapter explains how to describe the different elements making up a GAP model. Description is provided on the use of: Equipment data Entry in general 149 Wells 156 Separators 230 Joints 247 Pipelines 251 Tanks 304 (Reservoirs) Flares and Vents 314 Pumps 315 Compressors 326 Sources/Sinks 341 Inline elements 348 Inflow elements 378 Groups 379 Flowsheets 384 These elements can be found on the main toolbar.

2.5.2 Equipment Data Entry Screen Format The main data entry screen is the Summary Screen, a master section from which all equipment data can be entered.

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Enter the screen by double-clicking the left-hand mouse button on any equipment icon on the GAP drawing. This will take us to a screen that allows us data entry / results display for that particular well. The input screen for all the equipment has the same general format, though the data entry headings/ formats vary from one to the other. The following diagram shows the data entry screen for a well.

The screen consists of three parts: The Navigator (Equipment List) The Section Buttons The Action Buttons 2.5.2.1 The Navigator - Equipment list On the right-hand side of the screen below is a list of the equipment making up the GAP network.

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The equipment in the screen can be listed in four different ways, simply right clicking on the list: Separator down sort Tank up sort Alphabetical sort by equipment label Sort by equipment type As in the example above, we have used “Equipment Type Sort”. The default is “Separator down Sort” i.e. hierarchically going from the separators down to the wells and tanks. The user may change the way the equipment is sorted in the list by clicking the right-hand mouse button in the window to produce the relevant menu. Equipment is accompanied by a tick or a cross indicating the validity of the data associated with the item. When first entering the screen, the piece of equipment selected 1990-2011 Petroleum Experts Limited

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is highlighted in the system window . 2.5.2.2 Section Buttons For each piece of equipment the data is sub-divided into these three sections. Summary Input

Master section from which one can access all the others Accesses all the sections where data can be entered for the particular element (for example: IPR, VLP, etc. for a well) Section where the calculations results are reported Each section can be accessed by means of the correspondent button at the bottom of the screen.

Results Section buttons

2.5.2.2.1 Summary The Summary contains information about each element of the network (for example, a well, a joint, etc.). Label Name Mask Comments Data Summary

Name that appears in the GAP main screen (network drawing) Extended name Options to disable the element Comments on each element can be entered Section containing the links to all the input screens. The number and type of sections vary depending on the element.

Other sections vary depending on the element in consideration.

2.5.2.2.2 Input Button Clicking the Input button takes us to the input data screens as shown below.

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On this screen, it is possible to see various tabs, where the input data is entered. The number and type of available tabs depends on the equipment type. For example, in the case of a well, the input data includes the inflow and outflow data, along with constraints and any tank connections etc. When one of these tabs / buttons is selected, a child screen appears where relevant data can be entered.

2.5.2.2.3 Results Button Clicking on the results button display the calculation results for the specific equipment as shown below

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There are two tabs available for results buttons, one for each calculation type available in GAP: Network Solver Results Prediction Results

Tab reporting the results of the latest Solve Network calculation performed Tab reporting the results of the latest Prediction calculation performed

2.5.2.3 Action Buttons On the screens shown above one can also find a set of buttons that perform various actions, like Report, OK, Cancel etc. The buttons are what are referred to as action buttons in this manual. There are action buttons at every input data screen like the summary screen, various input screens and the results screen. The buttons that are displayed/ active on a screen depend on the equipment type and the GAP User Guide

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screen. These are described in detail on all screens description for all equipments. Some of the main buttons are described below. Run PROSPER / MBAL

In the case of a well, this opens a link to Petroleum Experts PROSPER program, to allow the setting up of PROSPER well models, the generation of performance curves, VLP, and IPR. For a tank, this opens a link to MBAL to allow the setting up of tank models OK Removes the dialog screen, saving all changes. This includes changes made in screens that have subsequently left by tabbing to another screen, or in wells that have been left by clicking on the well list box Cancel Removes the dialog, ignoring all changes. If any changes have been made, a Confirmation Message will appear Help Displays the help screen appropriate to the currently displayed screen or tabbed screen Revert This replaces the data of the current screen or tabbed screen with the data that was current when the screen was entered Validate Checks the data on the current screen or tabbed screen for validity. This takes into account the Prediction mode or whether or not the system is an injection system. If the data is not valid, the Validation Dialog will appear with diagnostic messages Calculate Available for well, compressor and pump elements when Summary and Input Section buttons are selected. For wells: If selected from the Summary screen, this allows to perform a VLP/IPR calculations If selected from the Input screen, this allows to estimate the liquid rate given the FBHP or viceversa For compressors and pumps: The Calculate button is accessible from the Input screen and allows to perform a calculation of the compressor/pump dP, head, power, etc. give the rate, PVT and inlet conditions. Plot Will produce a plot screen appropriate to the screen or tabbed screen being displayed (for example, an IPR plot for the IPR input screen). This is greyed out when there is no suitable plot Report Enters the GAP Reporting System. The report produced will depend on the currently displayed screen or tabbed screen (for example, an IPR report for the IPR input screen) Next (selected) These buttons can be used to navigate through the equipment list. Next Previous (selected) will move to the next piece of equipment in the equipment list. Previous will move to the previous piece of equipment in the list. If items are selected, these buttons will navigate between selected items Mark These buttons allow items to be marked for reference purposes during an editing session (for example, to indicate to the user that a well Mark All performance curve has been regenerated). Marked items appear with Unmark All their status (tick or cross) displayed in reverse v

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2.5.3 Wells

The modeling of the wells is the first part of building an accurate GAP field model. The rest of this chapter is devoted to a description of the data required for a complete well model in GAP. The data required for a well model in GAP model description depends on the mode in which GAP is running and the well model selection by user as described in the following sections. Like any other equipment, well data entry screens can be accessed by Double-clicking the left-hand mouse button on a well icon on the main GAP drawing, or Clicking on the appropriate well icon in the equipment list of the main data entry screen of any element on the network. On the well data entry / results screens, there are three sections (as explained in the details of format for equipment in the previous section). These are listed below: Summary Screen

Input Screen

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This allows the selection of well-model and well types, and also gives the status of various aspects of the well-input data. See the following section Includes tabbed screens for the following input fields: Control - dP Control - Artificial Lift control. The type of artificial lift control available will be depending on the well artificial lift method considered, as for example: Gas Lift Control (For gas lifted wells only) and ESP Control (For ESP Wells only) IPR Input VLP Input PC Data Input (For manual entry / generation of PC data for wells where PC model has been selected.) Constraints - General - Abandonment Downtime Coning Tank Connections February, 2011

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Production Data (Decline Curve prediction only) Schedule (Only if Prediction Selected in Main Option) Contains the following fields: Network Solver Results. Prediction Results

2.5.3.1 Well Summary Screen This screen is accessed by clicking on the Summary button of the well data entry screen.

Input Fields: Label

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Name

Mask

If blank, enter a short name or abbreviation to identify the icon on the screen Maximum of 32 characters allowed. Use this field to enter a full or descriptive name, if any, for the well. This name will appear in the reports generated by the allocation calculations This option allows a well to be added or omitted from the network database and consequently the calculations to establish a total system response. When the well is not to be taken into account in the system calculations, two options are available: Mask

Disable

Comments Well Type

(i.e. An 'X' over the well icon indicates that this well has been excluded from the system) where the well is excluded of the system but will be recalled during prediction if an unmask event appears in the well schedule (i.e. A double ‘X’ over the well icon indicates that this well has been excluded from the system) where the well will be excluded from the system whatever events are included in the well schedule

Enter any string of comments to give more detailed information about the well (for example, date shut-in, fractured, etc.) Specifies the type of well. This should be the first setting to make when creating a well, as the data required in the input screens depends on the well type. These options are available: Gas Injector Gas Producer Liquid Injector (NEW!!!) Oil Producer (Diluent Injection) Oil Producer (ESP Lifted) Oil Producer (Gas Lifted) Oil Producer (HSP Lifted) Oil Producer (Jet Pump Lifted) Oil Producer (No Lift) Oil Producer (PCP Lifted) Retrograde Condensate Producer Water injector Water producer SWAG wells can be modeled using liquid injector or gas injector well types. GAP handles simultaneously injection of gas and water. (NEW!!!) The Liquid Injector well type can be used to model injection of any liquid, like for example polymer or NGL.

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GAP can work with PROSPER .ANL or .OUT files. If a PROSPER .OUT or .ANL file for this well is available, the file name should be specified here. When GAP accesses PROSPER, the program will automatically open the relevant file Select one of the following: VLP / IPR Intersection PC Interpolation

Outflow Only – VLP

Outflow Only – PROSPER

Well rates will be calculated based on the intersection of VLP / IPR curves Well rates will be calculated based on a Performance Curve (PC), which is the curve representing the relationship rate vs tubing head pressure (or, more in general, pressure downstream the well, as defined in the well model). This option interpolates between the points of the PC. If this option is selected, The PC Generation selection will be active. NEW!!! The PC interpolation method allows to describe the PC by means of up to 20 points The well icon is only used to store the VLP curves that need to be pre-generated. An associated Inflow Icon will then provide the IPR in order to have a complete well model. Equipment set between the Well icon and the Inflow icon will be used to dynamically correct the IPR for pressure drop between the IPR and the VLP depths The well icon will not now store any lift curves. When a pressure drop calculation is required, GAP can calculate it dynamically using the equipment set in the PROSPER on line section. Please refer to the following sections for details

The outflow only models for well modeling have been introduced from GAP v5.0 onwards. They increase greatly the capabilities of GAP in terms of modeling smart well completions and multilayer systems (an example of multilayer model 743 can be found in the Examples Guide section) Rate Model (only when compositional model is enabled)

Rates can be defined in terms of volumes (at standard conditions) or mass. Defining the rates in terms of mass has got the great benefit of making the rates (hence the VLPs) process independent. This is because volumetric rates at standard depend on the process used to analyse the fluid, whilst mass is invariant, therefore does not depend on the process used. This option is particularly useful when coupling models having different reference paths to standard: using the mass one does not have to re-generate IPRs 1990-2011 Petroleum Experts Limited

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When Composition changes (only when compositional model with lumping/ delumping is enabled) Data Summary Area

and VLPs if the process changes. This option allows to lump/delump the composition entering the system through the wells

In addition to the selections discussed above, the well summary screen contains an input data summary area.

This gives details on the status of various aspects of the well-input data. It consists of various fields that correspond to different areas of well-input data. These screens have the following colour code: Red Green Cyan

if the data is invalid or missing if the data are valid indicates that information have been entered (e.g. a well constraint or dP control setting) These are coloured These are coloured Some icons may also be coloured , which

The icons that appear in this area are dependent on well model and Prediction Type (None / Material Balance / Decline Curve) selection. For the various fields, the following Status might be displayed: Tank Connections (Valid/Invalid) IPR Input Data (Valid/Invalid) VLP Input Data (Valid/Invalid) GAP User Guide

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Constraints Data (None/Some/Invalid) Controls (Set/Not Set) Pump Control (Artificially lifted wells only) (Set/ Not Set / Not Appl.) Performance Curve Data (Only for PC well model) (Valid/ Invalid) Gas Lift Control (Gas Lifted wells only)(Source name is displayed) Downtime (Set / None) Coning (Set / None) Scheduling (Set / None) By clicking on any of these fields, one can access the input data for the field. 2.5.3.2 Calculate On every well, in the action buttons one has access to a “CALCULATE” button. On the Summary screen, the Calculate is used to determine both IPR and VLP corresponding to one specific set of flowing conditions and then calculate the intersections between the curves. This is a rapid way to calculate the well performance for a specific set of flowing conditions.

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The user can plot the VLP/ IPR intersection by clicking on the Plot button.

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The Initialise from solver results can be used to recall the flowing conditions calculated during a Solve Network 434 calculation. This is useful when troubleshooting the well performance in the same conditions as in the main calculation. This will prompt the following VLP/IPR intersection screen:

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Note that when there are two intersections between the VLP and the IPR curve, GAP will by default pick up the intersection on the right hand side of the minimum exhibited by the VLP curve (as this is generally the stable rate whereas the left side intersection is the unstable one), except when the “Force Left Hand Side Intersection (Solver)” option has been selected. If GAP is expected to pick up the left side intersection, this can be done by selecting the “Force Left Hand Side Intersection (Solver)” as described earlier. On the VLP input screen, this button invokes the VLP calculation dialog. This enables to calculate the FBHP from the vertical lift performance curve of the well considered for specific sets of flowing conditions. The calculation screen appears as follows:

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2.5.3.3 Well Input Screens Appropriate tabs allow to enter all the well-input data required for system optimisation or prediction runs. The tabs are coloured according to the validity of the data on the corresponding dialogs. If the tab is green, then the data is valid for the current system set-up. If it is red, then the data is invalid or empty. If the tab is grey, then this tab is not applicable to the current model and so is inaccessible. The following represents the division of input data: Tank Connections

Enter/visualize tank connections

IPR Input

Used to enter/visualize IPR data, either for the well, or perlayer in a multi-layer well.

VLP Input

Used to enter/visualize the file that contains the lift curve data for the well.

Constraints

Use to enter/visualize the well constraints and abandonment constraints.

Controls

Used to enter/visualize control data for the well. This allows wells to be choked back to meet some throughput constraint, or for artificially lifted wells allows artificial lift control parameter, such as ESP frequency in ESP wells to be accounted for in optimisation.

Pump Controls Used to set the artificial lift quantity ad Fixed value (for example,mfixed gas lift injection rate) or Calculated by the optimiser. This section can be accessed from the Controls 1990-2011 Petroleum Experts Limited

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section PC Data

Use this to enter/visualize manually performance curve data, or to generate the data from VLP/IPR intersections.

Gas Lift Control

Used to set the artificial lift quantity ad Fixed value (for example,mfixed gas lift injection rate) or Calculated by the optimiser. This section can be accessed from the Controls section

Production Data

Enter/visualize the production data for the well, for decline curve predictions.

Downtime

Enter/visualize the percentage of time a well is offline.

Coning

If the well has gas coning the input data may be specified in this screen for each layer.

Schedule

Enter/visualize the Schedule for changing constraints, masking/ un-masking wells during prediction

Apart from the screen inputs as described in the following sections, there are various action buttons like OK, CANCEL etc. that appear in these screens. Their function is the same in every screen.

2.5.3.3.1 Tank Connections This section contains the list of all the tanks (MBAL models) connected to the particular well.

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Use the buttons to create connections or disconnect a well from a tank. 2.5.3.3.1.1 Multi-Layer Case

In this case, it is simply required to make connections using the two list boxes: the breakthrough constraints and perforation depths are entered in the Well IPR screen. Connected tanks are assigned to single layers of the model automatically; the tank name, which has been assigned to a specific layer, is displayed in the Well IPR Input screen.

2.5.3.3.2 IPR Input This screen allows the input of well inflow performance data on a per-layer basis. For a multi-layer well, any number of separate inflow performances can be modelled (a well model can be producing from as many distinct layers as the well has in reality).

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The IPR data can be transferred from PROSPER using the “Generate” function of GAP. If the user chooses to enter the data manually (IPR may have not been generated with PROSPER for example) then this can be done as well. (NEW!!!) IPR’s can now be generated with different PROSPER files for each layer by associating different PROSPER model to the each layer's inflow The IPR data input is divided into four tabbed screens as shown in the example below.

These are: Ipr Layer More... Prod Data

Grid View GAP User Guide

Individual layer input data like PI etc Data for defining relative permeability and layer breakthrough (water / gas) parameters (only if decline curve is selected as tank model) section defining the well GOR and WC (or WGR in case of gas) versus reservoir pressure or cumulative production Screen where a summary of all layers is tabulated and the individual IPR February, 2011

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data can be plotted against each other To define the conditions at which the layer is abandoned (production is shut down)

The data input for all the four sections of the well IPR input us described below: 2.5.3.3.2.1 Ipr Layer input data

In this screen, the input data can be defined, which are needed for generation of an IPR curve for each layer. The data input screen is divided into four sections. These are: Select Inflow Performance Input Fluid Properties Input PROSPER File for IPR Select This section has the following sub-menus: Layer List Box Layer Type

Mask

Use this to select the layer for which data is to be entered. When the list is produced, each layer appears in the drop down list with 'Invalid' or 'OK', representing the status of the IPR layer data (Available only for multi layer IPR Producers except WATER producer and injection Wells) This can be Oil, Gas, or Condensate. When a well is created, the layer type is set to reflect the well type: however, the layer type can be changed by selection from the drop down list. is possible to temporarily exclude the selected layer from the IPR by selecting Exclude from System from this drop-down list box

Switching to the More Input Screen will display data related to the layer that has been selected in the layer input screen. Inflow Performance The data items shown in this dialog depend on the well type, the layer type and the prediction (None / Material Balance / Decline Curve) mode. In a multi layer model, data may be entered on this dialog or in the IPR Input Grid View, which displays all layers simultaneously. Tank Connection

In a multi layer model, this gives the label of the tank to which the selected layer for which input is being entered is connected. The layer-tank connections are assigned automatically when a tank is connected to a well and are fixed throughout the life of the well. It is 1990-2011 Petroleum Experts Limited

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possible that the tank may be assigned to a different layer if the user chooses to do so IPR Type Select from the combo box the type of the IPR curve. The current choices are: Straight Line + Vogel (Oil and Water Producers / Water Injectors). Forcheimer (Gas / Condensate Producers / Gas Injectors) Forcheimer Pseudo-Pressure (Gas / Condensate Producers / Gas Injectors). This method uses the classic Forcheimer equation solved with a pseudo-pressure method rather than with a pressure square method. C and n (Gas / Condensate Producers / Gas Injectors) Table Look Up (All wells) The “Table Look Up” utility has been included in the IPR types for allowing an easy link between GAP and Reservoir Simulators. It stores the IPR information generated by the reservoir simulator as a table with oil, gas and water rates as a function of flowing bottom hole pressure (FBHP). IT SHOULD ONLY BE USED FOR THOSE APPLICATIONS. IPR dP Select here whether there is to be a manual offset from the reservoir pressure by checking the box. If the box is checked, enter the appropriate dP in the entry field. The IPR dP is used when the datum for the reservoir pressure in the well model is significantly different to the datum used in the reservoir model. The IPM dP corrects the reservoir pressure coming from the reservoir model to the well model datum. Permeability (Production systems only & NOT for Table Look Up) Correction with This is used to correct the absolute permeability of the layer as the pressure declines in a prediction. Enter the quantity N in the equation: Pressure kp

Cross Flow Injectivity Index

k0

1.0

p0

p

Cf

N

where, p is the layer pressure, kp is the layer permeability at pressure p , k0 is layer permeability at pressure p0 and Cf is the formation compressibility (Production systems only & NOT for Table Look Up) This is only applicable to multi-layer models. In cases where there is crossflow between layers, it is possible to specify here the injectivity index to be applied to the layer when cross-flow rates are calculated. The crossflow injectivity index represents the rate of injection in the reservoir should the bottom hole pressure be greater than the reservoir pressure. In other words, the crossflow injectivity index represents the IPR curve for negative flow rates.

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If the value of the crossflow injectivity index is not specified, the rate of injection in the reservoir will be governed by the Productivity Index (indicating that the production capacity of the reservoir is the same as the injection capacity). Should there be any studies made on the injectivity index for the stated reservoir, then this may be used to define the Crossflow injectivity index. The use of Crossflow Injectivity Index may lead to large cross-flow rates and potential instabilities in any prediction run as these rates are held constant over a time-step. In the case of gas wells and retrograde condensate wells, the corresponding IPR model (that is defined in the IPR type section) will be used instead of the productivity index. Only the primary coefficient of the IPR description is required in this case: the other (non-Darcy coefficient or n) is set to zero.

IPR Match

A combination of high instantaneous rates and large timesteps may cause large cumulative volumes of fluid to be transferred in a reservoir over the timestep. This will lead to unrealistically high reservoir pressures to be calculated. For wells with cross flow between layers it is recommended to use small step sizes in prediction mode. Selecting Match IPR on the IPR Input screen to display the following dialog:

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Test Layer Pressure When an IPR transfer from PROSPER is done, this screen is populated with data from the PROSPER IPR section. Test Water Cut See the Relative Permeability Section that follows for more details about how these values are used to apply correction factors to the IPR Test Points These fields hold the set of test points of measured rate and flowing bottom hole pressure. Rate and pressure can be entered by hand, or pasted from the Windows clipboard or directly from PROSPER’s IPR screen. Click Match and GAP will calculate the well productivity (or injectivity) index and AOF (or whichever coefficients are required from the IPR model). Click OK and the P.I. and the rest of the data will be passed GAP User Guide

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back to the well IPR screen. When an IPR is generated, the reservoir pressure and PVT information (e.g. GOR, Water Cut) are used in the calculation of an IPR.

Gravel Pack

Fluid Properties

Different results may be obtained in IPR generation when a tank is connected to a well and thus uses the tank’s PVT calculation, compared to the situation where the well is isolated and GAP uses its own calculation. GAP models Gravel Packed completion as in PROSPER. More detailed information about this model is available in the PROSPER user Guide. When the IPR is generated from a PROSPER file that contains a Gravel Pack completion, the Gravel Pack information are transferred from PROSPER to GAP. It is then possible to sensitize on Gravel Pack parameters in GAP. When the system is solved, GAP calculates the pressure drop across the Gravel Pack (accessible under the layer results). It is then possible to constrain the well production based on: The maximum gravel pack casing velocity The maximum gravel pack screen velocity The maximum gravel pack delta P (for producer wells) This section contains the fluid PVT properties, which are used during the Solve Network calculation. The properties are updated automatically during a Prediction, based on the data coming from the connected reservoir model (be this MBAL or a third party numerical simulator) PVT Data (NOT for Water Producers)

Use Tank Impurities PROSPER File for IPR

Enter: Oil / Condensate API Gas Gravity Current Water cut/ WGR Current GOR /CGR Enter water Salinity Impurity Data Mole % of CO2, N2, and H2S in gas phase can be specified (NOT for Prediction modes “None” & “Decline Curve”) If the ‘Use tank impurities’ box is checked, GAP will use the values from MBAL tank model and the impurity input data will be made unavailable For multi-layer well, it is possible to import the specific PROSPER file corresponding to each specific layer. When the option "Generate | Generate Well IPRs from PROSPER..." is used, GAP calls all those PROSPER files to generate in one go all the different layers' IPRs

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The Composition button allows to enter/visualize the composition for the well.

This is available when one of the compositional options are selected. The Composition Button allows to visualize the fluid composition.

Use Original Composition

By ticking this box the original composition entered in the well IPR section will be used for the calculations, overriding any composition coming from MBAL or the Working composition present in the well IPR section

The IPR Input windows contain the following action buttons.

The action buttons have been explained in detail previously 154 and have here exactly the same role: OK / Cancel / Help / Revert / Validate / Calculate / Plot / Report. The following action buttons are particular to the Input section, and their roles are described below: Plot GAP User Guide

Displays the Plot screen with the IPR plot for this layer (or the well in a February, 2011

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single layer model). The Match data (if present) is also displayed. In case of Grid View it displays the IPR of all layers and the total IPR of the well as well Displays the IPR Calculation screen. This allows rates to be calculated from flowing bottom hole pressures or vice versa for this layer (or for the well in a single layer model) See description below

From MBAL It is possible to transfer data from existing material balance models to well models inside GAP . VLP, IPR and relative permeability data can be transferred. This action button takes us to the screen that allows the import of well data from MBAL models as shown in the following screen:

On the left hand side, the MBAL files associated with the tanks in GAP are opened and lists of either history or prediction wells can be displayed, depending on the option chosen. 1990-2011 Petroleum Experts Limited

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On the right hand side, all the GAP wells along with their Layers are displayed. The user selects a layer in the MBAL list and a layer in GAP list. This gives the following two transfer options: IPR Rel Perm

To transfer the layer IPR To transfer the MBAL layer relative permeability data

If the user selects a well on both sides the following transfer option is available as well: VLP

To transfer the VLP data from the MBAL prediction well to GAP well

The actual data transferred will depend on the type of item selected in the MBAL list (e.g. tank IPR data will include the tank starting pressure and PVT data, whereas well IPR data includes the PI). At the bottom of the MBAL item list, is a “New Model File” button. Pressing this allows the user the access to MBAL files that might not be associated with the current GAP model and from the data can be transferred. Note that new files are not stored when the screen is cleared and must be reloaded when going into the screen on subsequent occasions. The details of data transferred using this facility are: IPR

GAP User Guide

This transfers IPR data from the MBAL item to the GAP target. The data transferred is as follows: From a tank: Starting pressure, Starting temperature, Impurity data (% H2S, N2, CO2 & water salinity), Gas gravity, Oil/condensate gravity, GOR/CGR. From a well: PI (Darcy coefficients, C and n), Layer type, PI Relative permeability correction (oil layers only), Perforation depths, Breakthrough constraints, Match data, February, 2011

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Test water cut / layer pressure. Transfers lift curve data to the well in question. This is only possible if the data has been imported into the MBAL well model in *.tpd format Transfers either the tank or the well relative permeability depending on the source type

2.5.3.3.2.2 More Layer Data

This is the second screen in the IPR input. It has the following sections: Layer Selection Relative Permeability

This is the place where the current layer is selected. This by default is the same layer as selected in the first screen (NOT for Injectors and Water Producers). See description below:

Relative Permeability Section The fields available are: Prediction Fractional Flow Rel. Perm

Here, we define the set of relative permeability that GAP uses for: 1. Calculating water cut and producing GOR (CGR/ WGR in gas / Condensate) wells during prediction (Material balance). 2. Calculating the changes in the well PI corresponding to due to WC and GOR change in all cases (No prediction/ Material Balance/ Decline Curve). Effectively, as the WC and GOR change, the fluid mobilities will be modified. The Options available are: From Tank Model

Shift Rel

(Available only for Material Balance Prediction) GAP will take relative permeability and data from the tank associated with the layer considered (MBAL Model) From GAP will use the relative permeability defined entered under Rel Perm 1 or 2 the Edit button. These rel perms can be entered by hand or transferred from MBAL by means of the button From MBAL (located at the bottom right of the screen). In both cases From Tank Model and From Rel Perm 1 or 2 the relative permeability curves are defined as Corey functions (ref. MBAL user Guide) From (see below 180 ) the user can enter directly the WC and the GOR as a function or time, pressure or cumulative production Table 1 or 2 The option “Shift Rel Perm to Breakthrough” is used to smooth the set of 1990-2011 Petroleum Experts Limited

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Perm to Breakthrough

relative permeabilities of water or gas, after the breakthrough occurred (see "Breakthrough and Perforation Depths" section hereafter). For instance, if this option is turned off, and if the gas breakthrough occurs at Sgb>Sgr, the relative permeability of the gas goes straight from zero to Krg_0 (cf. following sketch).

PI Correction for Mobility

It is possible to trigger this option on by selecting the “Yes” option in the corresponding scrollbar. If this option is set to ‘Yes’, the PI will be corrected for mobility change as the water cut changes. A test-water cut and a test pressure have to be entered. The test water cut and the test reservoir pressure are used to determine the water saturations (Sw) and oil and water viscosities. So is calculated as described in the Vogel correction depending on the options as indicated later. With the use of relative permeability curves, the test mobility can be calculated from: M test

K rw

K ro

w

o

At a particular reservoir pressure and water cut, the current mobility (M) can be calculated using similar formula. Based on the two calculated mobility values, the corrected productivity index will be: PI

PI test

M M test

And this value of corrected PI will be used to generate the new IPR GAP User Guide

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(Available Only if Mobility correction for PI is on) If this option is set to ‘Yes’, the relative permeability values that are used for PI mobility corrections are calculated using the effect of reduced oil/ water relative permeability caused by the presence of free gas down hole. It requires the entry of a test GOR value. The GOR entered is taken as the total produced GOR. Based on the PVT, a free gas saturation Sg is calculated. The Sw is then calculated on the basis of the test water cut and test reservoir pressure specified. So is derived from the following relationship: So

1 Sw

Sg

Once the phase saturation and viscosities are known the PI is estimated from total liquid mobility ratios as indicated above. In case this option is set to ‘No’ The oil and water mobility values are calculated on the basis of the assumption that the free gas down hole is zero. The oil saturation is then calculated as So

Brakthroughs and Perforations

1 Sw

Based on these phase saturations, the PI correction is made from mobility ratios as indicated above. Test Layer (Only for Oil producers) Pressure / Water Cut This is only available when mobility correction to PI option is set to ‘Yes’ Test GOR (Only for Oil producers) This is only available when Vogel correction for GOR is set to ‘Yes Edit Rel. Perm This displays the Relative Permeability input screen. The button is coloured according to the validity of the relative permeability data. The user can enter the relative permeability data here. It is important to notice that for both Prediction Fractional Flow Rel Perm and Prediction mobility Correction Rel Perm sections, two sets of relative permeabilities can be specified, Rel Perm 1 and Rel Perm 2 (ONLY for Material Balance Prediction) Here enter the perforation depths and following break-through conditions (if any) Gas Saturation or Gas Contact (Oil layers only) ; as soon as the OilWater contact and Gas-Oil contact predicted by MBAL reach those 1990-2011 Petroleum Experts Limited

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depths, the breakthrough is triggered Water Saturation and Water Contact (OIL / GAS/ CONDENSATE layers). Oil Saturation (CONDENSATE Layers ONLY). Top and bottom perforation depths (Perforation depths are currently used only when performing gas coning calculations)

Entering the Fractional Flow rel perms as Tables (NEW!!!) It is possible to enter directly the profile of WC and GOR (or WGR for gas) as a function of time, reservoir pressure or cumulative production. To do that, select from the drop down menu the option "from Table 1 or 2", as shown below:

Accessing the Edit button will allow to enter the required fractional flow table:

In the Primary Column section select the basis for the fractional flow curves (time, pressure or Cumulative Production). 2.5.3.3.2.3 Production Data

This option is active only when Decline Curve is selected as tank model. For Prediction modeling, GAP requires the current GOR and Water Cut for each well in order to calculate the well behaviour for some future condition. In Decline Curve prediction GAP interpolates a decline curve table of GOR and water cut as a function of reservoir pressure, GAP User Guide

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which is entered here. If using Decline Curves for prediction, click the Prod. Data tab to access the well production table, and enter the data as in the following example:

Select the layer for which to enter production data from the list box at the top of the screen. For single-layer wells, the only layer is available. For a full complement of production data, GAP required production data for every layer that has valid IPR data. The required input fields are: Current Layer Pressure Interpolate on

Reservoir pressure at which to evaluate GOR and Water Cut Curves can be expressed as function of Reservoir Pressure or Cumulative Production

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Calculate Plot

Calculates the water cut and GOR for the Current reservoir pressure Displays the production data in graphical form. Use Variables on the Plot screen to switch between GOR and water cut

2.5.3.3.2.4 Tight Gas IPR

As opposed to the other pseudo-steady state IPR models, the Tight Gas IPR model is transient. This inflow is driven by the rate history and the reservoir model i.e. permeability, drainage radius... IMPORTANT: the reservoir model is created within the well IPR section, and therefore the Tight Gas well cannot be linked to any reservoir models in GAP. The Tight Gas model is selected from the Summary section of the well screen, as shown below:

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IPR LAYER section The inputs required for the IPR section of the Tight Gas well are:

Where, in addition to the fluid properties entries: The reservoir characteristics are entered separately for each well. Note that the Drainage Area Radius entry should be a result of the Type Curve Analysis, that can be carried out in MBAL. The Darcy and Non-Darcy Skins are the skins relating to the transient inflow equation: 1442T n m Pi m Pwf Q j Q j 1 PD t dn t dj 1 SQn DQn2 kh j 1 as S and D factors respectively. The "Current Time" input data is only used when the Network is solved at a particular date. In that case, the time since the production started is calculated based on the difference between the "Current Time" entered and the "Start of Production" entered. For prediction

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runs, the time since production started is calculated based on the current prediction time. The time can be considered as "Normal Time", "Pseudo Time (Pwf)" or "Normal Time (Pbar)". The dimensionless time td in the equation above is:

td

0.000264 kt 2 ct i rw

where the subscript i refers to the evaluation of these parameters at the initial pressure. The time t can be considered as: The "Normal time" (time since the production started) The "Pseudo Time (Pwf)": t

t

ct

i t0

dt ct Pwf

where the subscript Pwf refers to the evaluation of these parameters at the bottom hole pressure. The "Pseudo Time (Pbar)": t

t

ct

i t0

dt ct

P

where the subscript P"bar" refers to the evaluation of these parameters at the average reservoir pressure. More information about this model and its theory can be found in the MBAL User Guide. PROD DATA section (optional) In this section, a production history can be entered. It will be used to update the IPR for the current first timestep of the prediction:

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2.5.3.3.2.5 Grid View

To display total IPR plots for a multi-layer well, go to the IPR Grid View and press Plot from that screen. This will display the plots for individual layers, as well as the overall IPR over all layers. This is only available in a multi-layer well model. This screen also has the summary of all layer IPR data entered. The column headings are the same as those displayed in the basic IPR Input screen (multi-layer case). Action Buttons Plot

Plots the total well IPR, in addition to the individual layer IPRs for all valid layers. This will show a plot looking like this:

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Calculate

Report

Invokes the IPR Calculation screen. This performs rate/bottom hole pressure calculations based on the total well IPR, rather than the individual layer IPRs Invokes the standard GAP report generator. This produces a report for the total well IPR in addition to the individual layer IPRs (valid layers only)

2.5.3.3.2.6 Abandonment Section

This section enables to define abandonment constraints (i.e. maximum GOR, maximum WC, minimum Liquid Rate) for the entire well or the layer considered. If these abandonment values are met by the well during the prediction, the well will be definitely closed by GAP, meaning that the well will neither be automatically re-opened by GAP if the abandonment constraint is not met anymore, neither re-opened through the schedule.

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Wells can be abandoned based on: Maximum Gas Oil Ratio Maximum Water Cut Maximum Water Gas Ratio Minimum Liquid Rate Minimum Oil Rate (NEW!!!) Minimum Gas Rate

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2.5.3.3.2.7 Note on water injector's IPR

Here is the IPR screen displayed when the well model is "water injector":

The “Frac PI” and “Frac dP” input data are entered to model fractures. The following “Water Injector” IPR sketch illustrates how these two values are taken into account.

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Bottom Hole Pressure

Fractured dP i.e. “Frac dP”

Initial Reservoir Pressure

Normal PI i.e. “P.I.”

Fractured PI i.e. “Frac PI” Water Rate

The normal P.I. entered or calculated (if the IPR is generated from PROSPER) is used up to a bottom hole pressure equal to the initial reservoir pressure + the Frac dP value entered. From this point, the Frac PI is used. 2.5.3.3.3 VLP Input This screen allows the user to specify the data file associated with the well considered and containing the VLP table. If the table does not exist, it can be generated using the “Generate” feature of GAP. Details on the VLP generation are given in the VLP/IPR generation 388 section. The screen appears as follows:

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In this screen, the following input fields are available: VLP File Name Turn off if unstable NEW!!! Force Left Hand Side Intersection (Solver) Allow Left Hand Side Intersection (Optimiser) Safe VLP/IPR intersection Import/Export Inspect Generate VLP Information VLP File Name

In this field, a valid vertical lift performance (VLP) file is expected. The data file is a binary format file. The file can be generated in the following ways: 1. Using the “IMPORT” button as shown. This button allows import of the following lift curve formats: · *.TPD – Petroleum Experts General GAP/ MBAL Format. (These can be generated in PROSPER well models). · *.MBV – Petroleum Experts MBAL Format. (These can be

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generated in PROSPER well models). · *.ECL – Eclipse Format. (Generated by any nodal analysis well modeling package). · *.VFP – Eclipse Format. (Generated by any nodal analysis well modeling package). Once files with this format are imported, GAP automatically creates a *.VLP file and saves it for its own use. 2. Using the “BROWSE” button to pick up an existing VLP File. 3. Using the Generate button available in the VLP screen. This Generate button is a shortcut to the GAP main VLP generation menu.

Import

Export Turn off if unstable Force Left Hand Side Intersection (Solver)

4. Using the “Generate VLP from PROSPER” command in the Generate menu in main screen to batch generate the lift curves for all wells in the model with valid PROSPER files. The label alongside VLP file names will read either OK or Invalid. An invalid flag means that an invalid file has been selected (e.g. a gas VLP for an oil well), or that the path name is incorrect. Import allows to import in GAP files containing the VLP sets in format . tpd (exported by PROSPER), Eclipse .ecl and .vfp and Sensor .snr. The file .tpd is exported from PROSPER and is the recommended format to import, as these files contain a list of wellhead temperatures along with the fluid rates A VLP table can be exported as a *.TPD file for use in other wells or applications using the “Export” button This option allows to shut down the well as soon as the well becomes unstable (VLP and IPR intersect on the left-hand section of the VLP) Selecting this option will force the solver to select the well rates (calculated by VLP / IPR intersection) on the left hand side of the minimum stable rate as indicated by the VLP. The two plots below describe this phenomenon. Right hand intersection: Stable Well Production

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Left hand intersection: Unstable Well Production

Allow Left Hand Side Intersection (Optimiser) Safe VLP/IPR intersection

Inspect GAP User Guide

Checking this option will allow the optimiser to use the unstable part of the lift curve in the search for the optimum solution. This can be the case in wells which are coning gas for instance, where a higher Well Head Pressure will result to higher liquid rates (as the cone is eliminated) This is a new feature in GAP 5.0 and is an improvement in the case of complex lift curves (primarily for gas coning wells). As the GOR for these lift curves is a function of the liquid rate (and given by the coning model), this intersection method provides a much “safer” way of getting an intersection that the default method. It is, however, much slower than the default method and should only be used when absolutely necessary This option allows to view the tables of VLP curves and also to plot February, 2011

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them, which can be used to quality check the sets of VLPs in use This option accesses the VLP generation dialog (see below 402 ) In this section information concerning the VLP curves used are displayed: Type of well (indication of the VLP format) Calculated Variables (sensitivity variables included in the VLPs Surface and Vertical Correlation (NEW!!!): multiphase flow correlations used to produce the VLP set in use

In case where a new well model is constructed, it is recommended to go through “Generate” menu option as this ensures that the correct variable formats that are needed for the well performance in GAP are picked up.

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. 2.5.3.3.3.1 Inspection of VLP Data

The VLP data that is associated with a file in the form of a VLP file can be inspected manually by selecting the "Inspect" button from the VLP Input screen. The VLP tables look as shown below:

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This is a lookup table of VLP results. The left and right hand columns give the VLP curves for the variable parameters highlighted (in reverse video) in the central columns. The data presented here is editable. It may be exported into a performance data file by pressing the Export button; this produces a File browser allowing to select the appropriate file destination. The variables that are a part of the VLP file depend on the type of well. For example this is a naturally flowing oil well VLP table. It is recommended to check the VLP data manually before, running the prediction cases in order to check the data validity. On this screen, there are a few action buttons. These are: OK Cancel Validate Plot

GAP User Guide

Validate and go back to the previous panel Disregard all changes and go back to the previous panel To visualize eventual out-of-range data The "Plot" button can be used to plot on the same graph some VLP curves and to verify the quality of the curves:

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The Variables menu can be used to select the sensitivity cases to plot. Help

To visualize this panel

2.5.3.3.4 Well Constraints

2.5.3.3.4.1 General Constraints

Well constraints can be used to control a well to meet physical or contractual requirements forcing the well to produce at maximum potential or below it. Select the Constraints tab to display the well constraints screen as follows:

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Maximum Temperature Minimum well flowing bottomhole pressure Maximum Draw down / Reservoir Pressure

Well optimisation weighting Well shut in priority

Maximum GAP User Guide

Rates are controlled based on this maximum temperature at the wellhead Well is shut in/choked back if the flowing bottom hole pressure falls below this value GAP will ensure that the flowing bottom hole pressure does not vary from the reservoir pressure by more than this amount. In a snapshot calculation, the reservoir pressure entered in the IPR section will be used to calculate the constraint. In a prediction run, the reservoir pressure will continually be recalculated for each time step. In the case of a multi-layer well, the reservoir pressure reference is taken from the extrapolation of the total IPR to zero rate This is a multiplier that is used on the well production during the optimisation process. It essentially weights the well in the optimisation purposes (Gas lifted systems only) If GAP has to shut in wells during optimisation, then this value sets a ‘shut in priority’ for the wells considered: if a value greater than one is entered, then this well will have a greater chance of being shut in during optimisation (all other conditions being equal). If no entry is made, this value defaults to unity (NOT FOR GAS WELLS) February, 2011

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Liquid Production / Injection Minimum liquid production rate/ Injection Maximum gas production / Injection Minimum gas production / Injection Binding (Yes / No) Potential (Yes / No)

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Well production cannot exceed this maximum. Naturally flowing wells will be choked back using dP Control if necessary to meet the maximum rate constraint. Artificially lifted wells will be controlled using both dP control and artificial lift specific controls to meet the maximum rate constraint (NOT FOR GAS WELLS) GAP will try to produce this minimum rate irrespective of oil rate optimisation considerations. Use this to set production targets for particular wells (GAS WELLS) Sets upper production limit for the well considered (GAS WELLS) GAP will try to produce this minimum gas rate irrespective of optimisation considerations This option can be used to set whether a particular constraint is binding or not (see binding/not binding topic 121 ) Includes or excludes the constraint it relates to in the potential calculations

GAP has the capacity of optimising the production from gas lifted wells by altering the amount of gas lift gas injected in the well. If the gas lifted control has been selected (refer to the Gas lift control 204 section) the constraints screen will allow entering relevant constraints for gas lifted wells. The following constraints are available for gas lifted wells control: Maximum gas injection rate Minimum gas injection rate NO-CLOSE minimum gas injection rate

Used to set field operational limits for injection gas GAP leaves the well shut in unless it deserves at least this volume of gas to optimise production Forces GAP to allocate this volume of gas irrespective of whether the well should be allocated gas to optimise production or not. Used to model particular field operating practices e.g. to ensure flow stability

GAP has the capacity of optimising the production from diluent injection wells by altering the amount of diluent injected in the well. If the diluent control has been selected the constraints screen will allow entering relevant constraints for diluent injected wells. 1990-2011 Petroleum Experts Limited

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The following constraints are available for diluent wells control: Maximum diluent rate Minimum diluent rate Maximum motor power Minimum motor power

Used to set field operational limits for diluent injection GAP leaves the well shut in unless it deserves at least this volume of diluent to optimise production Set the field operational limits relative to the maximum motor power used in the well considered Set the field operational limits relative to the minimum motor power used in the well considered

GAP has the capacity of optimising the production from pump lifted wells by altering the frequency of the pumps in the network. The constraints screen will allow entering relevant constraints for pump lifted wells. The following constraints are available for pump lifted wells control: Maximum Pump Frequency (ESP Wells) Minimum Pump Frequency (ESP Wells) Maximum Power Fluid Rate (HSP and Jet Pump Wells) Minimum Power Fluid Rate (Jet Pump Wells) Maximum Speed (HSP and PCP Wells) Minimum Speed (HSP and PCP Wells) Maximum motor power Minimum motor power Maximum power fluid surface pressure (HSP wells) These constraints will be available through the Constraints | General screen, as illustrated below for an ESP well.

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However, it is possible to note that for pump lifted wells, it will be possible to specify tables of pumping characteristics vs. minimum and maximum pump rates given by the pump manufacturer. These tables will be used to check make sure the pumps will operate in a suitable range of rates for a given frequency in the case of ESP wells for instance. The following tables can be entered, according to the type of artificial lift system selected: Table of Table of Table of Table of

Operating Frequency vs. Minimum Pump Rates (ESP Wells) PCP Speed vs.Minimum Pump Rates (PCP Wells) Power Fluid Rate vs. Minimum Pump Rates (Jet Pumps Wells) Rotational Speed vs. Minimum Pump Rates (HSP Wells)

To enter these constraints tables, click the Pump subsection tab in the Constraints menu, as illustrated below for an ESP Well.

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2.5.3.3.4.2 Abandonment Constraints

Abandonment constraints can now be set from the data entry screen and on a per-layer basis. To enter abandonment constraints, click the Abandonment tab of the constraints screen. On the resulting screen, the user may enter abandonment constraints for the entire well, or for individual layers (in the multi-layer model). Abandonment constraints are used as criteria to shut the well in during a prediction run: for example, if one sets a maximum GOR abandonment constraint, then the well will be shut in during a prediction run if the produced GOR exceeds this value. The following abandonment may be set: Maximum GOR Maximum WC Maximum WGR Minimum Liquid Rate Minimum Oil Rate

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Minimum Gas Rate Enter into the fields the abandonment constraints that one wishes to apply.

2.5.3.3.4.3 Symbols

When setting Constraints, the program will plot in the network picture two arrows pointing towards the element.

General Constraints Abandonment Constraints

red arrows pointing to the element blue arrows pointing to the element

2.5.3.3.4.4 Notes on Constraints

When setting up the model, it is recommended to start with the minimum necessary number of Constraints. In this way the user has the possibility to validate that the model performs as it is supposed to. After that, the number of Constraints can be increases, if necessary. GAP provides with a physical model of the whole production/injection system. This means that any constraint imposed in the system should reflect the physical reality of the field. For example, if a well at its maximum production cannot produce more than 1000 STB/day oil rate, it would not have sense to set up a minimum production constraint of 2000 STB/day, as this would be impossible to achieve. Based on these considerations, it is recommended not to use minimum constraints during a prediction run. In the case where minimum constraints cannot be physically honoured 1990-2011 Petroleum Experts Limited

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(because the system not necessarily can deliver the minimum liquid rate as the reservoir depletes, for example), the optimiser will try to honour an infeasible situation. This may provide unreliable results for the whole system. If the objective is to shut down the well if this cannot produce a minimum amount, this can be achieved by setting up an Abandonment Constraint of minimum rate in the Abandonment section: as soon as the well production decreases below the set minimum abandonment constraint, the well will be closed.

2.5.3.3.5 Controls The Controls section allows to set choke values for the current well, and artificial lift controls (in the case of an artificially lifted well). 2.5.3.3.5.1 Symbols

When activating a control (dP Control or Artificial Lift quantity control) the program will display in the network picture the following symbols: dP Control

A thin solid red circle is set around the well icon.

Artificial Lift Control

If no circle is around the well, the control is set to None or Fixed Value A thin rounded square is set around the well icon. If the square is dashed, the control is set to Fixed Value If the square is solid, the control is set to Calculated

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2.5.3.3.5.2 dP Control

The Controls section allows to set choke values for the current well, and artificial lift controls (in the case of an artificially lifted well).

dP Control options None Fixed Value

Calculated

There is no choke at the wellhead. Equivalent of having the well fully open Allows to enter a fixed dP at the wellhead to model the effect of a choke. Fixed pressure option includes the quantity specified in the next field as the wellhead choke dP GAP optimiser is used to calculate the pressure loss in the wellhead choke to maximise production and at the same time honour constraints

The choke defined in this section is at the end of VLP curves. If the curves include pressure losses up to the wellhead, the choke is at the wellhead level. If the curves include Pressure losses in the downhole equipment and a flow-line up to a manifold, the choke is then considered to be at the end 1990-2011 Petroleum Experts Limited

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of flow line. In the Calculated Option , the results screen has a choke-calculator, which allows the user to estimate the choke setting that corresponds to the dP calculated using the Perkin' s choke model (SPE20633). 2.5.3.3.5.3 Gas Lift Control

Gas Lift Control Control Mode

Fixed Gas Lift Gas Injection Rate Fluid Properties

GAP User Guide

(Fixed / Calculated) The gas lift gas rate injected in gas lifted wells can be controlled by GAP by setting the Control Mode field to Calculated. Minimum and Maximum gas lift gas injection rate need to be specified The value of gas lift gas injection rate that GAP will use in calculations for fixed gas lift gas rate control mode The fluid properties of the gas lift gas used can be specified. If compositional PVT modeling is enabled, this section will allow to access and edit the composition of the injected gas

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2.5.3.3.5.4 ESP Control

ESP Control Frequency Control Fixed Frequency

(Fixed / Calculated) The operating frequency of ESP wells can be controlled by GAP by setting the Frequency Control field to Calculated The value of fixed frequency that GAP will use in calculations, for fixed frequency control

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2.5.3.3.5.5 Diluent Control

Diluent Control Control Mode

Fixed Diluent Rate Fluid Properties

GAP User Guide

(Fixed / Calculated) The diluent rate injected in diluent injected wells can be controlled by GAP by setting the Control Mode field to Calculated. Minimum and Maximum diluent rates need to be specified The value of fixed diluent rate that GAP will use in calculations, for fixed diluent rate control mode The fluid properties of the diluent used can be specified, as well as the injected fluid temperature. If compositional PVT modeling is enabled, this section will allow to access and edit the composition of the injected fluid

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2.5.3.3.5.6 HSP Control

HSP Control Control Mode

Rot.Speed

(Fixed / Calculated) Rotational speed in HSP wells can be controlled by GAP by setting the Control Mode field to Calculated The value of fixed rotational speed that GAP will use in calculations, for fixed rotational speed control mode When the Control Model is set to Calculated, Minimum and Maximum rotational speed can be specified

Min Rot. Speed and Max Rot. Speed Power Fluid Mode Enables to specify if the power fluid is commingled with the production fluid or in a closed loop. If the power fluid is commingled with the production fluid, its impact on the pressure drop throughout the system will be taken into account Fluid Injected The fluid properties of the power fluid used can be specified by defining in the Edit List table the fluid type as Water or Other

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2.5.3.3.5.7 Jet Pump Control

Jet Pump Control Control Mode

(Fixed / Calculated) The power fluid rate injected in jet pump wells can be controlled by GAP by setting the Control Mode field to Calculated. Minimum and Maximum power fluid rates need to be specified Fixed Power The value of fixed power fluid rate that GAP will use in calculations, for Fluid Rate fixed power fluid rate control mode Power Fluid Mode Enables to specify if the power fluid is commingled with the production (Available only in fluid or in a closed loop. the Well Summary If the power fluid is commingled with the production fluid, its impact on the pressure drop throughout the system will be taken into account screen) Fluid Properties The fluid properties of the power fluid used can be specified, as well as the power fluid temperature

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2.5.3.3.5.8 PCP Control

PCP Control Speed Control

Fixed Speed

(Fixed / Calculated) The operating speed of PCP wells can be controlled by GAP by setting the Control Mode field to Calculated The value of fixed speed that GAP will use in calculations, for fixed speed control

2.5.3.3.5.9 Fluids Property Setup

Fluid Properties Setup (i.e. For all artificially lifted wells using either an injection fluid or a power fluid) For artificial lift systems associated with an injection/power fluid, it is possible to alter / modify the fluid properties used in the Control screen, as illustrated below for a gas lifted well. The Control screen allows to change/ define the gas lift source properties that are associated with this well.

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The source names are set up in the Injection Fluids dialog, which can be accessed from the Options menu. It can also be invoked by pressing the Edit List button of this screen. Select the required Gas lift source in the Enter Choice drop down list box. The properties of the source will be displayed for convenience in the Fluid Properties area beside this. The composition of the source can be displayed by selecting the Composition button at the base of the screen (when compositional tracking is enabled). This can only be edited through the Injection Fluids screen. The colour of the button indicates the validity of the source composition. If compositional tracking or full compositional modeling are enabled, this must be valid for the calculations to be performed. 2.5.3.3.6 PC Data When the well mode is set to PC Interpolation, in the Input section the PC Data tab is available. This tab contains all the information on the PC (ref. Summary screen for definition of PC 157 ), which can be entered by hand or calculated on the basis of the well VLP/IPR.

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The quality of the PC used can be verified by accessing the menu Results/Plot Performance Curves, as shown in a later section 501 . This feature allows to spot if VLP and IPR have been correctly generated. 2.5.3.3.6.1 PC Generation

This screen is used to generate a set of well performance curves using the VLP and IPR data entered in the Well IPR Input screen and the VLP file entered in the Well VLP Input screen. It is called from the Well PC Data screen from the 'PC Generation' button. Input Fields Reservoir Pressure IPR dP Shift PVT Data Manifold Pressures

The current reservoir pressure If enabled (from the Use IPR dP checkbox), offsets the Reservoir pressure used by the IPR These fields hold the PVT data for the IPR, ie Water cut, GOR, Oil gravity and Gas gravity for an oil well These fields hold the generate wellhead pressures. For non-gaslifted wells, clicking the Automatic WHP button will allow PC generation using a set of pressures which cover the wells operating range. 1990-2011 Petroleum Experts Limited

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The data items displayed on this screen are those that are global to the well; thus for a multi layer well with more than one valid layer the reservoir pressure, PVT data and impurity data (for example) can not be displayed. The reservoir pressure, PVT quantities etc are the same as those entered in the Well IPR Input screen Command Buttons Generate Ok

Cancel Help

Use this button to calculate the performance curves. An informational message will be output when the process is complete Use this button to leave the screen and save all changes that have been made. The data generated in any 'Generate' process will be written to the Well PC input dialog Use this button to leave the screen and ignore any changes made Use this button to access this screen

2.5.3.3.7 Downtime This screen allows entering the well downtime for a prediction run. Production constraints are evaluated using the potential well rates. Cumulative production is calculated from the instantaneous rate times the well efficiency factor (100% - down time). The well down time factor can be entered in the field provided. The efficiency can also be adjusted in the Prediction Wells screen that is in turn accessed from the Prediction Forecast set-up screen. For decline curve prediction models, the well efficiency is also included in the Well Production Data screen.

2.5.3.3.8 Coning (For Oil Producers Only) Coning of gas from a reservoir can be accounted for in the GAP well models. Two scenarios are possible: 1. The well layer is not linked to any MBAL model. In that case one can directly switch the Mode from None (no coning) to one of the coning options 2. The well layer is linked to a MBAL model. In that case, the Mode option will be active only of the coning model has been enabled in MBAL first See the MBAL manual for more information on the theory behind gas coning modeling. GAP User Guide

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Mode

This list box contains a list of all valid layers, along with the name of the tank to which they are attached, and whether or not gas coning is set up in the tank model. Select from the list the layer for which one wishes to enter data Select this check box to enable coning for the layer. Coning will then be applied in prediction, provided that the coning data is validated successfully. Two options are available: Analytic

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This allows to match an analytical method to match the profile of Liquid Rate vs Produced GOR This allows to directly enter in the program the table of Liquid rate vs Produced GOR. In this case up to 10 points of the table can be entered

These are repeated from the "IPR | More..." screen. Enter the top and bottom perforation depths for the well relative to surface The gas-oil contact depth tracked in the MBAL model during a prediction run overwrites this field. It may be used following a 1990-2011 Petroleum Experts Limited

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Matching Data/ Test Data

Results

Note

snapshot reload, or whenever a performance curve is regenerated outside of a prediction, to adjust the gas-oil contact depth from the tank model These are used to evaluate the coning coefficients F2, F3, and the exponent. Enter up to three match points (liquid rate against producing GOR) and test values for gas-oil contact, water cut, and layer pressure. When the Match button is selected, the values for the coefficients will be entered automatically into the dialog fields The coning coefficients F2, F3, and the exponent may be entered by hand (without performing a Match). They must be present for the data to be validated prior to performing a prediction run When the Validate button is selected, validation information for the current layer will be displayed. The dialog tab will be coloured according to the validity of the entire coning data set - any invalid or missing fields in any layers will be picked up. Only those layers that have coning enabled will be included in the validation

2.5.3.3.9 Schedule (ONLY for Prediction) This is used during the prediction to change the well constraints or to include or exclude the joint from the system at a specific time in the forecast.

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Since IPM version 6, this is possible to schedule any variable change, using the variable OPENSERVER access string. The variable OPENSERVER access string can easily been accessed "Ctrl+Right clicking" on the variable tab.

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2.5.3.4 Outflow Only Well This method is a feature that offers greater flexibility in terms of modeling downhole networks (multilayer systems and smart well completions). This option can be activated from the well summary screen:

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Two methods are available for the Outflow only well: VLP PROSPER

The dP along the wellbore is determined on the basis of VLP curves The dP along the wellbore is calculated using PROSPER online

These two options enable to specify the method by which the pressure drops in the Outflow part of the well will be calculated, either using VLP tables or calculated “on the fly” using the PROSPER online options. In the latter case, the well equipment and temperature options are defined inside GAP and used whenever a pressure drop calculation needs to be performed as opposed to simply looking up the pre-calculated pressure drops from the VLP table. The IPR part of the well needs to be considered separately using an inflow icon, described in Inflow section 378 . Only limited information can be entered in the outflow section, relating exclusively to the well outflow performance, and therefore the VLPs. In the main GAP screen, the outflow only well is identified with the following icon:

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2.5.3.4.1 Outflow Only - VLP If the VLP only case is selected, then the well icon will only include the lift curves, no IPRs can be specified. In the Input Data section only data relevant to the outflow part of a well can be entered. In the VLP section:

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A VLP file can be imported if it already exists or can be generated using the “Generate” feature from the GAP main screen (Please refer to VLP generation 402 section for details on the VLP Generation). The functions of this screen have already been explained in the previous section of this chapter.

2.5.3.4.2 Outflow Only - PROSPER This option can be selected from the well summary screen. The purpose of the Outflow Only – PROSPER model is to enable the user to specify the well equipment in GAP, or import them from an existing PROSPER file. The pressure drops in the well bore can then be calculated whenever needed by GAP rather than being looked up from a table. There are two main advantages for using this method: The advanced thermal options of PROSPER are now available in GAP for the pressure drop calculations The pressure drops are calculated with the PVT of the fluid that goes into the wellbore, which may be changing over time. This is particularly useful in multilayer systems in which the rate contribution from each layer changes significantly over time (depending on the rate of depletion of each). When lift curves are used, one can only assume the contribution of each layer and use one set of PVT as the rate of depletion cannot be decided before a prediction is done. The well equipment can be setup in two ways, either directly from an existing PROSPER file or entered directly in GAP.

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2.5.3.4.2.1 Importing the equipment data from PROSPER

This can be done by selecting the “Import” button, as shown previously. The program will then prompt with a file selection menu where an existing PROSPER file can be imported. Selecting “Open”, GAP will transfer the equipment data from the PROSPER file into the equivalent screens in GAP:

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The correlations used in PROSPER along with the corresponding match parameters will also be transferred, as seen from the screen above. One can then go through the screens (starting from “Options” in order to validate that the data transferred are OK). Selecting “Options” will prompt the “Options” screen of PROSPER:

In this screen the Options selected in the PROSPER file can be seen. Moving to the PVT section:

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The PVT used in PROSPER are transferred along with the PVT Matching parameters for the different correlations. The Pressure drop calculations will be done based on the fluid entering the well at every timestep. This PVT section is only used to match the correlations that will subsequently be used to provide the PVT parameters for the pressure drop calculations. The GOR and gravities entered here will therefore be ignored during the calculations, only the matched (or original in the case of no matching) correlations will be used. Following the PVT, the equipment section can be accessed:

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Here one can specify the equipment based on which the pressure drop calculations can be done. This section is the same as in PROSPER with screens for entering the deviation survey, any surface equipment to be included in the pressure drop calculations, the well equipment and geothermal gradient (these data for the Rough Approximation temperature method only). Further screens will be made available if the Improved Approximation or Enthalpy balance methods are selected. Note on Surface Equipment: There is no need to include any surface pipelines in this section as they can be described separately in GAP. The user has the option of including a single flow line leading from the well-head to a manifold in either program depending on the objective of the model. However, pipelines that carry fluid originating in more than one wells need to be described as separate GAP pipelines. The next section is related to erosional velocities and solids transport. Selecting the “Solids” button will prompt the following screen:

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Density of sand

Used to calculate the Maximum Grain Diameter that can be transported based on the velocities in the well Sand production Will be used to determine the erosional velocities in the pipe rate and S factor using a Conoco model (Improvement to API14 E) C factor Will be used to compute erosional velocities based on the API 14E recommendation. A value of 400 is recommended as opposed to 100 recommended by the API as this was found by various researches to be very pessimistic Turner Constant Used for liquid loading calculations. Turner proposed this constant to be 20.4 but after extensive testing, we have found that 2.04 gives much more realistic results These constants can be left to their default values or changed depending on the users engineering judgement. The last section in the PROSPER on line data has to do with matching of the pressure drop correlations:

In the case where test data are available, these can be entered and all the quality check and matching features of PROSPER can be utilised to QC the data and match a correlation, making it unique for the well in question. Selecting “Correlation Matching” for the downhole equipment, the test can be entered and then the quality check and matching procedure described in PROSPER can be followed, leading to a consistent and predictive well model. More information are available on this topic in the PROSPER user Guide. Having finished this section, the well summary screen can now be revisited and therefore ensure that the Outflow only well model is valid:

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2.5.3.4.2.2 Entering The Equipment in GAP Directly

Selecting the “Edit” button in the screen shown above will allow the user to enter the well equipment data directly in GAP, without the need to specify a PROSPER file at all: This button will prompt the Equipment screen and all the sections described above can be visited and populated with data. Matching of the PVT and pressure drop correlations can also be done in this section as described previously.

2.5.3.4.2.3 Completing the Outflow Only Well - Inflow Performance Setup

In order to complete an Outflow only well, one or more corresponding inflows need to be specified, with or without equipment between the inflow and the well. One example of a three layer system is shown below: 1990-2011 Petroleum Experts Limited

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Completed well model with Outflow only well icon and inflow icons.

Outflow Part

Inflows

An example of how to set up a model with Inflow and Outflow elements can be found in the Examples Guide 743 . 2.5.3.5 Well Results Screen This screen contains all the results from allocations or predictions that pertain to the current item. To switch between item results, use the list box on the parent screen: Network Solver Results Screen

The results screen is divided into two sections. The first is the Network Solver results:

Prediction Results Screen

and the second is Prediction results, which is only valid if a prediction run has been carried out:

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2.5.3.5.1 Gradient Results In the case where the well is modelled as an Outflow only well – PROSPER the results after a solve network or a prediction calculation will include a new screen where the gradient results can be seen. This can be accessed from:

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Selection of this will prompt the Gradient calculation screen of PROSPER that will display the gradient traverse calculations corresponding to the results:

This list includes up to 77 variables that are calculated using the gradient traverse features and includes erosional velocity, holdup, mass flowrates etc. 2.5.3.5.2 Well Layer Results In the case where the well is connected to more that one layers as shown below:

The results can be seen as total for the well (as shown in the previous section) or on a layer by layer basis. When the prediction is done, the “Layers” button will appear:

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This allows access to the results of each layer:

Crossflow is calculated based on the IPRs of each layer and will be shown as negative rates in the layer results.

2.5.3.5.3 Reporting Results In these sections all the results related to the performance of the well in question can be accessed and exported using the “Report” Button highlighted above. Selecting the “Report” button will prompt the following screen:

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If results need to be exported to Excel, the “Clipboard” and “Tab Delimited” formats can be chosen. Selecting “Run Report” will then allow the program to place the results on the Clipboard and then pasted into Excel.

2.5.4 Separators (Production / Injection)

In GAP, separators are nodes where a pressure value is fixed regardless of the rate through them. It does not necessarily denote the presence of an actual separator in the system; it could be any fixed pressure point in the network. The effect of the P and T conditions at various separators in the network on fluid formation volume factors etc. is accounted for using the PVT data from the wells or reservoirs providing the fluid to the separators. In a single GAP model there can be more than one separator defined, each with its own fixed pressure value. Each of these separators can have independent constraints. For systems with more than one separator, make sure that each separator has a different name to enable easy identification in reports. The pressure of the separator when solving the system or doing predictions is not specified in the separator icon itself. It is set under the Solve Network or Material Balance Prediction Forecast screens. The following help section is valid for both production separators and injection manifold. In input screens where there is a difference, this is clearly pointed out and explained.

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Double clicking on the separator icon will provide access to the Separator Summary screen. There are three sections, which are itemised below: Summary Screen This allows the selection of separator types, and also gives the status of various aspects of the separator input data Input Screen Includes tabbed screens for the following input fields: Constraints Separation ( Only for Production Separators) Injection source ( Only for gas, water and steam injection manifolds) Schedule (Only if Prediction Selected in Main Option) Results Screen Contains the following fields: Network Solver Results. Prediction Results NOTE The separated fluids can be picked up and sent through separate networks to other separators. This operation can be done using sources connected to the separator icon, as shown below. The source can be defined as separator oil, gas or water to pick up the corresponding phases. This means that up to three sources (one for oil, one for gas and one for water) can be connected to a separator.

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2.5.4.1 Separator Summary Screen When double-clicking on a separator in the system view, the main data entry screen initially displays the separator summary screen.

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The following describes the fields that may be entered on this screen. Label

Name Comments Mask

Defaults to the name supplied in the Label dialogue box when the item was initially added to the system. If blank, enter a name or abbreviation to uniquely identify the icon in the screen display of up to 12 characters in length. Keep labels short to improve drawing readability Enter any name or description to see as a heading for this separator in the reports Enter any string of comments that gives more information about the separator; e.g. date brought on stream, etc. This option allows a separator to be included or omitted from the network database and therefore from the calculations for establishing the total system responses. An 'X' over the icon indicates this separator has been masked (excluded from the system). Three options are currently available: Include in system Mask Disable

Separation Type

The item is enabled and open to flow in the main network Excluded from the system unless it is scheduled to come online during a prediction If an item is disabled, it will not come online, even if it is scheduled to do so during a prediction

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Data Summary Area

Oil Injection Manifold NEW!!! This field contains the summary of the data that is needed in the input screens. This also indicates, if the current data is valid or not. In case the separator is an injection manifold, the data summary screen contains an additional input field as shown below for defining the source of the injected fluid.

2.5.4.2 Separator Input Screens The separator input screens that need to be defined, depend on the type of separator (production / injection) and the type of prediction (None / Material balance / Decline Curve.). The following sub-sections explain the details of these input screens.

2.5.4.2.1 Separator Constraints Constraint parameters are optional. They may be used to enter the specific production/ injection or physical constraints of a separator. Selecting the constraints tab of the input data section yields the following screen:

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Constraints (as described under the data input section) should not be entered until the entire GAP model has been validated against measured production data (provided these are available). Operational, environmental or mechanical constraints of a separator can be modelled by entering the appropriate constraint values. Minimum values can be used to give a production stream priority during optimisation runs. When left blank, GAP assumes there are no constraints for this item. The program will not check that conflicting constraints have been entered. When constraints are active for any node in the system, the constraint symbol is shown above the element icon (see next figure). For instance, a separator with constraints will have two arrows pointing to it. Same for any other piece of equipment with constraints in it:

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Separate constraints are available for Total Gas through the separator (i.e. sum of produced and gas lift gas) or Produced gas only. The total list of constraints that can be set at this point is: 1) Maximum water production/ Injection 2) Maximum gas production / Injection 3) Maximum liquid production / Injection 4) Maximum oil production / Injection 5) Minimum gas injection rate 6) Minimum liquid production / Injection 7) Minimum gas production / Injection 8) Maximum power 9) Minimum pressure 10)Maximum pressure 11)Maximum CO2, H2S, N2 12)Minimum Oil Specific Gravity 13)Maximum Gross Heating Value 14)Maximum Specific Gross Heating Value 15)Unscheduled production deferment GAP will automatically track the gas impurities (CO2, H2S, N2), even if the compositional tracking option is switched off. In the case where the tracking option is active, then the impurities from the composition will override the values from the BO PVT model. System constraints, i.e. for the total combined production for all separators in the system, are entered under Constraints/ System Constraints. Please Refer to Constraints 118 tables section for details.

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2.5.4.2.2 Separation (PRODUCTION Separators ONLY) This is required only for production separators. At each separator level, we may remove a percentage of gas and water from the separator, by using the following screen.

The separated fluids can be picked up and sent through separate networks to other separators. This operation can be done using sources connected to the separator icon. Please refer to Sources section 341 for details.

2.5.4.3 Injection Fluid Details (INJECTION Man.Only) This is required for gas, water or steam injection systems. The properties of the oil / gas / water / steam (quality) that are to be injected are specified in the list of injected fluids, along with the composition if compositional tracking is enabled.

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If one selects the Edit List button, the following screen appears:

This screen can be used to create as many fluid sources as required. One can specify a particular fluid for injection that can be then selected from the list in the drop down menu of the separator injection screen: GAP User Guide

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Note on "Steam Injection Manifolds": The internal steam calculator will automatically calculate the saturation pressure and minimum enthalpy given the injection temperature (inputted) and the steam quality (inputted in the Fluids' list). 2.5.4.3.1 Schedule (PREDICTION Cases ONLY) This is required in case during the production the separator constrains / back pressure change. All the constraints that are variable in main separator screen can be changed during the prediction, using the schedule.

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2.5.4.3.2 Steam Stream The steam Injection manifold is selected from the Separation Type drop down menu:

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A steam stream needs to be created in the Injection Fluids' list, using the "Edit List" button from the Input | Fluid section of the injector icon:

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In this list, a steam "Type" fluid can be created; the steam quality needs to be entered. The steam calculator can be used to calculate the steam properties at different pressures and temperatures. It will be noticed that the steam calculator can either been accessed from the Injection Fluids' screen or from the Input | Fluid screen of the injection icon. The steam calculator is the same as the one implemented in PVTP.

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Steam Calculator The option "Calculate Range" is used to calculate the PVT steam properties at different values of pressure and temperature. The option "Calculate Single" is used to calculate the PVT steam properties for a given pressure and enthalpy (or temperature and enthalpy).

Calculate Range

The following screen is used to enter the temperature and pressure ranges to calculate the steam PVT properties for. When the option "Pressure Split Range for Table" is turned on, the program will use the "Lower Half of Range Step" as step size for the lower pressures (for half of the number of steps specified).

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Hit the button "Calculate" to access the calculator screen, from which hit again the "Calculate" button to trigger the PVT calculation.

The Button "Plot" can be used to plot PVT properties, such as saturation temperature as illustrated below:

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Enter the Pressure and Enthalpy (or Temperature and Enthalpy), and the steam calculator will calculate: the density / enthalpy / viscosity / Cp and Cv of the liquid or gas if the fluid is SINGLE PHASE the saturation temperature (or saturation pressure) / latent heat and steam quality (as well as the different phases' PVT properties) if the fluid is TWO PHASE

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2.5.4.3.3 Oil Injection manifold NEW!!! This new element allows the user to define an input of oil coming from a source at fixed pressure, just like water injection and gas injection sources.

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2.5.5 Joints

The joint is a point in the network where two or more different pieces of equipment connect together. Each joint is a solution point within GAP. As with separators, there is no compulsory data entry for joints. This following section describes the possible input options for Joints. Like any other equipment entry the joint data entry/results screen has three sections (as explained in the details of format for equipment in Equipment data 149 section).

2.5.5.1 Joint Summary Screen The Summary screen appears in the main data entry screen when double-clicking on a joint in the system window:

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This screen is similar to the Summary screen of all equipment nodes and as such its contents will not be explained every time. Please refer to the Separator Summary screen section for details. Lumping Rule (Present only when Compositional PVT is enabled) It defines which lumping rule is adopted for the fluid flowing through the joint

2.5.5.2 Joint Input Screen The various input categories are displayed in the tabs at the bottom part of the screen. Navigate through the input screens by clicking on the appropriate tab. The tabs conform to a general colour-coding scheme: Green indicates that the data associated with the screen is valid; Red indicates that the data is not valid. When the tab is greyed out, the tab is not accessible due, for example, to the model selected.

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2.5.5.3 Joint Constraints Joint constraint parameters are optional. They may be used to enter the specific production constraints of a joint and the pipeline it feeds into. Joint constraints are entered on the following dialogue box:

Enter the maximum levels of production that GAP can use while optimising production. These are usually determined by the physical or mechanical constraints of the manifold or associated pipes. To force production from a group of wells even though this may not maximise oil production, use minimum constraints. When left blank, the program assumes there are no constraints for this item. The full list of constraints that may be set is: 1) Maximum water production/ Injection 2) Maximum gas production / Injection 3) Maximum liquid production / Injection 4) Maximum oil production / Injection 5) Minimum gas injection rate

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6) Minimum liquid production / Injection 7) Minimum gas production / Injection 8) Maximum power 9) Minimum pressure 10)Maximum pressure 11)Maximum CO2, H2S, N2 12)Minimum Oil Specific Gravity 13)Maximum Gross Heating Value 14)Maximum Specific Gross Heating Value Use constraints with caution. Constraints set for one item can conflict with those set for other system components. Maximum and Minimum constraints that are set close together are effectively blocking optimisation. Avoid using minimum constraints during a prediction. The minimum constraints will be honoured by the optimiser provided that the potential of the system can sustain production above the minimum. If the potential of the system is below the minimum, the optimisation will not be successful.

2.5.5.4 Schedule This is used during the prediction to change the joint constrains, include or exclude the joint from forecast.

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We will note that masking of joints in the schedule will cause all the equipment that can not produce into the separator to be masked as well.

2.5.6 Pipelines

Pipeline connections are represented by boxes drawn across the centre of the line connecting two joints. A pipeline is created by connecting two joints together. One joint is needed to specify the beginning of the pipe and another for the end. Connections between joints and wells have no input screens. For GAP calculations these are not pressure drop connections: No pressure drop calculations are run within an element to joint connection. Therefore, these connections will not be displayed on the screen as pipelines. The following screenshot illustrates the difference between pipeline connections (i.e. joint to joint connections) where the pressure drops are calculated and simple links (i.e. joint to element connections) where no pressure drop calculations are run.

The pipeline data entry / results screen has three sections (as explained in the details of format for equipment in Summary section 149 ). These are itemised below:

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Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the method used to calculate pressure drops, the input data and the flow correlation in use for the pipeline. See the following section for details Depending on the calculation method used, the required input data will change. Please refer to the sections below on the data required for each method Contains the following fields: Network Solver Results. Prediction Results

GAP allows to obtain all the details of the results of a pipeline calculation ( see below 271 ), like PVT (viscosity, FVF, densities, etc.), velocity, slug calculation and many other profiles along the pipeline. 2.5.6.1 Pipeline Summary Screen This is displayed by default when double-clicking on a pipe icon in the system window. For example:

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This screen is similar to the Summary screens of all equipment nodes. Please refer to the Separator Summary 232 screen section for general details. Input data: Label

Name Mask

A maximum of 18 characters is allowed. It defaults to the name supplied in the Label dialog box when the item was initially added to the system. If blank, enter a name or abbreviation to identify uniquely the icon on the screen display Enter any name or description to see as a heading for this pipe in the reports This option allows a joint to be included or omitted from the network database and therefore the calculations for establishing the total system responses. An 'X' over the icon indicates that this well has been masked (excluded from the system). When a well is unmasked, all items above it in the network database up to its separator are automatically unmasked 1990-2011 Petroleum Experts Limited

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Comments Pipe Type

as well. Select: Include in system Mask (Excluded from the system unless it is scheduled to come online during a prediction) Disable (If an item is disabled, it will not come online, even if it is scheduled to do so during a prediction) Unlimited number of characters allowed. Enter any string of comments that gives more information about the pipe Pressure drops in the pipe can be calculated using three options (see below). One can use the internal correlations of GAP, using PROSPER in line or by the use of lift curves. Options on the summary screen will change depending on the method used. The following sections will describe each of these in detail

Pipe Type Pressure drops in the pipe can be calculated using three options. GAP Internal Correlations Lift Curves

Multiphase flow correlations are used for the pressure drop calculation

Sets of VLP curves can be imported (for example from PROSPER or from GAP Internal Correlations themselves) PROSPER on line PROSPER within GAP is used for the dP calculations One can use the internal correlations of GAP; PROSPER on line method or pipeline lift curves. Options on the summary screen will change depending on the method used. The following sections will describe each of these in detail. The two pressure drop terms (gravity, friction) are displayed in the results section. PROSPER on line allows to either generate lift curves for increased speed in calculations, or to be used as such and take advantage of the thermal models of PROSPER for accurate pipeline temperature predictions (Enthalpy balance or Improved Approximation options) 2.5.6.2 GAP Internal Correlations This section will describe the use of calculating pressure drops “on the fly” using the internal PVT and pressure drop correlations of GAP. Correlation

Correlation Coefficients

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Select from this drop-down list the correlation to use in the calculation of pressure drops. In the presence of match data, then the correlation selection will depend on the correlation that matches the data the closest These fields display the gravity and friction coefficients that are used in the calculation of pressure drops. These coefficients will be recalculated in the event that the user performs a Match calculation. For February, 2011

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Oil Viscosity Correlation

Oil Pb, Rs, Bo correlation

Gas Viscosity Correlation Emulsion

Lumping Calculation Mode Data Summary Area

255

a correlation that matches measured data exactly, both parameters should be 1 The oil viscosity correlation can be selected for each pipeline independently of the oil viscosity correlation entered by default under the System Settings (Edit | System Settings) In the current version of GAP the Egbogah et al. correlation for heavy oil viscosity is available The Bubble Point, Solution Gas Oil Ratio, and Oil FVF correlations can be selected for each pipeline independently of the correlations entered by default under the System Settings (Edit | System Settings). In the current version of GAP the Al-Marhoun correlation is available The gas viscosity correlation can be selected for each pipeline independently of the gas viscosity correlation entered by default under the System Settings (Edit | System Settings) It is possible to account for the effects of emulsion on fluid viscosity by ticking the Emulsion box. After that, a list can be accessed and edited, including all the emulsion viscosity data (active only when compositional model is enabled) This option allows to specify which composition to use for the main calculation. if is selected, the program will use the Lumped or the DeLumped composition as specified in the menu Options/Method This shows the status of the various aspects of item data. In the case of a pipe, there are only three such areas

2.5.6.2.1 Pipe Input Data If the link is to be used to model a section of pipe and to calculate pressure drops then pipeline geometry will be required. If the Calculation Method is Pressure and Temperature (as set up on the Options screen), then pipe Environment data is also required. All other data entry is optional; however, matching is recommended if possible. 2.5.6.2.1.1 Pipe Environment

GAP can calculate Pressures Only for each pipeline, or it can calculate both temperature and pressure. For the Pressure and Temperature case, the program requires information on the surrounding environment of the pipe, as well as a heat transfer coefficient to run the calculations. GAP uses this information to determine the rate of heat loss. The following is a typical data entry screen:

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Surface Temperature Overall Heat Transfer Coefficient Heat Capacities

Enter the temperature of the environment surrounding the pipe This value accounts for steady state heat transfer by conduction, convection and radiation. The HTC is referred to the pipe inside diameter Average values for Oil, Gas and Water. Note that the Cp of gas is a function of temperature and pressure and the value entered should be carefully checked - do not rely on the defaults

2.5.6.2.1.2 Pipe Description

Click on this tab to enter the geometry of a pipeline. Up to 25 pipeline segments can be entered. Pipe data must be entered from the Downstream (Separator) end to the Upstream (Wellhead) end. In this entry screen, begin at the top and work down to enter data, as shown in the following example:

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Pipe Description Input Columns Type

Length TVD

Diameter Roughness

Enter the kind of pipe or choke in use over this section. The available types are: Line Pipe Choke Coated Flexible Fitting The pressure drop calculations are performed in the same manner, irrespective of the pipe designation (Line, Coated or Flexible). Enter the total length of this pipe section. Equivalent lengths can be used to account for pressure losses associated with elbows, bends etc. TVD depth is the depth at the upstream end (closest to the well) of the pipe. This entry field will be changed to Depth Change should the “Enter Elevation As” option be switched to Segment Depth Change Enter the inside diameter of the pipe Enter pipe surface roughness. The default value of 0.0006 inches corresponds to stainless steel, but it can changed as necessary depending on the application 1990-2011 Petroleum Experts Limited

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Fittings

In the case where fittings are selected as part of the pipe equipment the Program will prompt a screen to choose the type of fitting. Selecting the “Choose” button above:

This screen is essentially a database with different K Values corresponding to the fitting to be modelled. The program will then use these K values in order to calculate the equivalent length of pipe that will give the same pressure drop as the fitting. The formula used is GAP User Guide

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Where: HL = Velocity Head K = Resistance coefficient v = velocity g = constant K-Values are defined as the “Resistance Coefficients”. Details on formulae and nomographs used can be found in Crane's book “Flow of Fluids through Valves, Fittings and Pipes” If a fitting cannot be found in the database, then the “Uselr Entered k Value” Option may be used in order to enter the K value directly:

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Heat Transfer Coefficient

If in the main program Options 70 the Improved Approximation is enabled, then in the description data the Heat Transfer Coefficient along the pipeline is required, as shown below:

The depth reference that was used in the PROSPER well models is unimportant as the connection between well and surface facilities is done with lift curves (a pressure drop

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for given GOR, WC, WHP etc). However, the elevation of the surface pipelines connected to each well must be entered with respect to a common reference in GAP. For consistency and ease in troubleshooting, we recommend that the user should enter all the depths in both PROSPER and GAP using the same reference point. Chokes are included in the pipeline data input section only to model a fixed restriction in the pipe. GAP optimiser will calculate the wellhead pressure drops required to meet system constraints. Include chokes in the pipeline description only when modeling the effect of a fixed restriction. Other Input Fields Rate Multiplies the pipeline fluid velocity by this value. Identical parallel pipes can be modelled by entering a rate multiplier of 0.5 Multiplier Max Length This is the iteration length used in the calculation of pressure drops over a pipe length. This should not need to be altered, unless the pipe under Step consideration is particularly long and the speed of calculation is particularly important Flow Type Either Tubing Flow or Annular Flow; if the annular flow is selected, it is asked to enter the tubing outside information (roughness and ID) as well as the casing inside information (roughness and ID) Correlations / Select an appropriate pipeline correlation from those available. The Coefficients correlation that is selected will be used in subsequent build operations, and if the correlation has been matched to existing data the calculated coefficients will also be incorporated (see below). The user may edit the coefficients by hand if required Match Click on this button to perform a pipeline matching to the available multiphase correlations. The button will be coloured green if there is no match data present, blue otherwise Swap Node This button can be used to swap inlet (upstream) and outlet (downstream) of a pipe work. Note that the labels of the upstream and downstream nodes are displayed. This display can be useful in building complex networks. The small white arrows in the pipeline icon denote the upstream and downstream direction of the pipeline. The node at which the arrows are pointing towards is the downstream direction and the node they are pointing away from is the upstream. Small arrows denote upstream to downstream directions. Here, J2 is the Downstream and this relates to the number on row 1 of the pipe description. The upstream joint refers to the number on the bottom of the description.

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COPY, PASTE, CUT, INSERT, DELETE ALL INVERT

Select the row number of the desired pipe element/s and click on particular button to perform the appropriate task

This option can be used to select all the points in the pipe element This option can be used to select all the other points than the one which is presently selected

NOTE Chokes are included in the pipeline data input section to describe the pressure drop due to fixed restrictions in the pipe, and should only be used to model existing systems. Delta P control should be used to have GAP calculate the unknown pressure drop required to satisfy a constraint, thereby modeling a variable choke function. Do not include a choke in the pipeline description in such cases. When GAP detects steam in the system (either coming from a source or an injection manifold), the U-value needs to be specified at the "Segment Type" level for all the pipelines in the system, even if the temperature model selected in the main option is "Rough approximation", as steam can potentially pass though it and the "Improved approximation" temperature model be used by default.

The following example illustrates how to define a pipeline in GAP. A pipeline is created every time 2 joints are linked. The depth reference that was used in the

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PROSPER well models is unimportant as the connection between well and surface facilities is none with lift curves (a pressure drop for given GOR, WC, WHP etc). However, the elevation of the surface pipelines connected to each well must be entered with respect to a common reference in GAP. For consistency and ease in troubleshooting, we recommend that the user should enter all the depths in both PROSPER and GAP using the same reference point. As an example the following sketch is used to represent a pipe description in GAP

NOTE: Please note that the above configuration can be merged in one single pipe; Up to 100 rows are available to enter pipe data . This will speed up the calculation since the are less elements interconnected in the system and in some cases avoid confusion with the linking nodes reference. The Upstream and Downstream side of the pipeline (for description purposes) will be determined by which joint one starts to create the link and will be represented by 2 little white arrows pointing to the downstream side. This Upstream and Downstream definition has nothing to do with the actual flow direction, as this will be ruled by the pressures in the system.

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upstream start at 0 feet

When describing consecutive pipelines, one should make sure that the consecutive pipelines have the same TVD at the linking joint. The end (Downstream) of one pipe should be consistent with the Upstream of the next pipe; in this example the linking node is J2, notice that downstream of pipe 1 TVD correspond with the Upstream depth of pipe 2

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To change the nodes (i.e. switch which joint corresponds to the top row and which joint corresponds to the bottom row) click on the ‘Swap Nodes’ button. Chokes are included in the pipeline data input section only to model a fixed restriction in the pipe. GAP’s optimiser will calculate the wellhead pressure drops required to meet system constraints. Include chokes in the pipeline description only when modeling the effect of a fixed restriction. 2.5.6.2.1.3 Pipeline Pressure Matching

This section explains how to enter actual production rates and pressures, and then adjust the pipeline pressure drop correlation parameters to achieve a match between model and actual values. For design calculations, an appropriate correlation must be applied without matching. By matching the pipeline pressure losses to real data, an accurate system model can be built all the way from the wells through the gathering system up to the production separator. Pipeline pressure drop matching is not compulsory before carrying out production rate or lift gas allocation calculations. However, in order to ensure maximum calculation accuracy it is recommended that the pipe matching step always be carried out whenever field data is 1990-2011 Petroleum Experts Limited

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available. A non-linear regression technique is used to adjust the selected pipe correlation to match the measured producing pressures. To begin the matching process, click on the Match button in the pipe description screen, as described above. The following screen will be presented:

To enter the pipeline match data, carry out the following steps: Ensure that the rate type selected is the same as the test data. Choose either Liquid Rates or Oil Rates. Enter the test points in the grid columns. Up to ten different points may be entered at a time. Match rows can be removed or added to the calculation by selecting the row and then clicking Enable or Disable as required. After entered the data, click on Match to proceed with the calculation. To perform the surface pipe pressure drop matching, carry out the following steps: Click Match from the pipe match data entry screen, as described above. A surface pipe match calculation screen will appear.

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Select the required correlations to match to from the list box: click All to select all the correlations. For horizontal flow lines, use a pipeline correlation. For vertical pipes, (e.g. platform risers), select a vertical flow correlation. Click Match to start the calculations. Up to 300 iterations are performed by the match routine; the process completes after 300 iterations or when the Match convergence criteria are satisfied. The results of the matching can be viewed by clicking the Statistics command button, as shown below:

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In this screen, the Reset buttons reset the fitting parameters for the given correlation to their defaults. Similarly, Reset All resets all correlations. The match parameters represent the corrections to the correlations that were required to achieve a match. Parameter 1 is the gravity term correction and Parameter 2 is the friction term correction. The calculated parameters for the selected correlation are used in any subsequent build process with this correlation. The gravity loss is zero for horizontal pipelines: therefore the gravity term cannot be matched. In such cases, Parameter 1 is left set to 1.0. Refer to the PROSPER manual for more details of the matching procedure. Repeat the matching procedure for each pipe until all pipes have been matched to real data. Provided that this step has been carefully carried out, the overall system model should not require further adjustment in order to match actual production and pressure data.

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2.5.6.2.1.4 Constraints

In this section the user can apply certain constraints on the pipeline, such as Max velocity, C factor and Line pressure. Please note that constraints with regards to rates can be set either at the upstream or downstream node (joint) of the pipeline.

2.5.6.2.1.5 Schedule (ONLY for Prediction)

This is used during the prediction to change the pipeline constrains, include or exclude the pipeline from forecast.

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Masking of Pipelines in the schedule will cause all the equipment that can not produce into the separator to be masked as well. Scheduling OPENSERVER Variables Since IPM version 6, it is possible to schedule any variable change, using the variable OPENSERVER access string. The variable OPENSERVER access string can easily been accessed "Ctrl+Right clicking" on the variable tab. For instance, it would be possible to schedule a change in the pipeline diameter t model a workover assuming the OPENSERVER Access String for the pipeline diameter is previously known:

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2.5.6.2.2 Pressure/Temperature gradient result After the Network Solver is run (or after a prediction snapshot is reloaded), pressure and temperature gradients calculated in the pipeline can be displayed. Right click on the pipeline and select "Show Gradient":

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Pressure and Temperature gradients can be displayed using the "Variables" option from the plot menu bar.

To view the detailed results of the pressure drop calculation, access the Pipeline Summary Screen, then Calculate. After that, select Initialise from Solver results to import the results from the Network Solver calculation. Then select Calculate: this will convert the pipeline temporarily into PROSPER on line and will enable to view detailed Gradient Results. The process is shown below:

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2.5.6.3 Using Lift Curves for the Pipeline Pressure Drops This section will deal with the input screens when lift curves are used for calculating pipeline pressure drops. When the lift curve option is selected, the user needs to choose a model for generating these:

There are four options in the drop down menu: External GAP internal Correlations PROSPER On line PROSPER file

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2.5.6.3.1 External This option allows the user to enter a lift curve file that has been externally generated. The file will need to be imported by selecting the lift curve button, as shown below:

In the screen that follows allows the user to import the lift curve file:

The “Import” Button will prompt a menu for selecting the file.

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The file can have the following extensions (as shown above): *.tpd *.mbv *.ecl *.vfp *.snr The *.tpd and *.mbv files can be generated by PROSPER. The difference between the two is that the *.mbv file does not contain any temperature information and should ideally be used only with a prediction in the MBAL software (as there is no surface network to carry temperature information through). The ecl and vfp formats are ones recognised by the Eclipse simulator. The snr format is one recognised by the Sensor simulator. Selecting one of these appropriate files will be imported into GAP and automatically converted into a *.vlp file. This is a binary file that GAP will use in the calculations. If this file already exists, then it can be imported by using the “Browse” instead of the “Import” button.

2.5.6.3.2 GAP Internal Correlations The purpose of this Underlying Model is to allow generation of Lift Curves using the Internal Correlations of GAP. The program will use the pipe description and correlations (matching included) that have been entered in the data input screens (see above 255 ). The advantage of this method is speed, as calculations do not need to be carried out during the prediction or solve.

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Upon selection of the Lift Curves tab (shown above), the user is prompted with the following screen:

As the file needs to be created, one needs to select “Generate” in order to get the following screen:

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The parameters for which the VLP curves will be created need to be entered under “Data”. Selecting the Fluid Type will automatically prompt the right parameters to use (for instance, in the case of "mainly liquid", these are Liquid Rate, Upstream Pressure, GOR, WC and Upstream temperature). The user can either enter the ranges manually or use the “Populate” Buttons on the bottom of this screen. It is important to notice that as pipelines can be flowing in two directions, the range of rate selected for VLP calculation should include both negative and positive rates, as in general the flow direction is not known before running the calculation. The use of negative rates will allow the program to run calculations even in the case the flow in not in the same direction as the pipeline convention (defined by the drawing in the pipeline description section). An illustration of entering negative rates is reported below:

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Selecting “OK” will lead the user back to the Generation Screen where selecting “Generate” will start the calculations:

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previously set to "Lift Curves". Please refer to the section "Batch Generation of Pipe VLPs 402 " for more information. 2.5.6.3.3 PROSPER on line The selection of this underlying method will allow the user to generate lift curves using the PROSPER on Line feature to create a model for the pipeline from GAP. Selecting the PROSPER on line method will prompt the following screen:

The main advantage of this method is that the user can generate lift curves by using the advanced temperature models available through PROSPER on Line The Edit Pipe button allows the user to create the pipeline model using the PROSPER on Line features. Please refer to the next section, called "PROSPER on line Pressure Drops 283 " for a detailed information on how modeling the pipe with PROSPER on Line. In term of Lift Curves generation, the method is then the same as the one described in the previous section called "GAP Internal Correlations 254 ".

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Selecting “Options” will prompt the Options screen of PROSPER:

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Under model, one can select three options: Rough Approximation Enthalpy Balance Improved Approximation A description of the input required for each follows.

2.5.6.3.4 PROSPER file The selection of this underlying method will allow the user to generate lift curves using an existing PROSPER file (with the pipeline only option). When this option is selected, the following screen should prompt:

The "Browse" button can then be used to attach the corresponding PROSPER file. In term of Lift Curves generation, the method is then the same as the one described in the previous section called "GAP Internal Correlations 254 ".

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2.5.6.4 PROSPER On Line Pressure Drops This option can be selected from the well summary screen:

Using this option will enable the user to calculate the pressure drops in a pipeline on the fly, using the advanced temperature options which were up to now only available in PROSPER. Traditionally, the temperature calculations in GAP were done using the rough approximation method. Now the user can do these using the Enthalpy Balance or Improved Approximation Method. The advantage of using the PROSPER on Line over lift curves are: No interpolation between lift curves if the exact conditions are not available is done. Instead of pre-specifying the PVT as is the case in the lift curve generation, the calculations are done with the PVT coming from the reservoirs depending on conditions. This is particularly important in multilayer reservoirs where the contribution of each reservoir can change over time. The advantage of using the advanced temperature models over the rough approximation method are: When pipelines are being designed, but no match data is available, the Rough approximation method is not sufficient as the heat transfer coefficient cannot be back calculated. The enthalpy balance method allows accurate calculation of temperature in this kind of scenarios. The drawback of using the Enthalpy Balance method is speed, as the method is computationally intensive. In the Examples Guide an example of PROSPER reference.

724

On-line Pipeline 724 can be used as

NOTE on CO2 injection models When modelling pipelines carrying CO2 for injection purpose, it is important to properly define the fluid options in the PROSPER on-line Options: Fluid type: Retrograde Condensate PVT Method: Equation of State The next section explains how to enter the pipe data using the "Edit Pipe" option:

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2.5.6.4.1 Edit Pipe entry The activation of the three temperature models (Rough Approximation, Enthalpy Balance and Improved Approximation) can be done from “Options”:

And then under “model” the user can select the temperature model:

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The "Equipment" is then customized accordingly to the temperature model selected, as described in the three next sections. NOTE: The Black Oil PVT correlations can be matched using the "PVT Matching" feature. More information about the PVT matching option can be found in the PROSPER manual. The "Solid" button allows specifying key parameters used in several complementary calculations in PROSPER (Maximum Grain Size Diameter, Erosional Velocity,Liquid Loading and Pigging). Multiphase Flow correlations can be matched to test data using the "Correlation Matching" feature. More information about the Multiphase Flow correlation matching option can be found in the PROSPER manual. The two matching parameters that result from the Multiphase Flow correlations matching procedure can be accessed clicking on "Correlation Parameters". "Correlation Threshold": It allows the user to specify alternative correlations to use for tubing or pipeline when the angle (from the vertical for tubing and from the horizontal for pipelines) exceeds a user-specified threshold value. This option is useful for modeling the riser for a long subsea tie-back or for a highly deviated surface pipeline. Enter the appropriate angles and correlations. Select Yes to the question Use 1990-2011 Petroleum Experts Limited

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Threshold Angle to enable the feature. When enabled, the calculation screens will indicate that this option is active.

2.5.6.4.1.1 Rough Approximation

If the Rough Approximation temperature model is selected, then the user needs to enter basic information about the pipeline as well as the average surrounding temperature under equipment. This model is essentially the same as using GAP internal correlations:

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2.5.6.4.1.2 Enthalpy Balance

The enthalpy balance method will calculate the heat transfer coefficient as a function of heat losses due to Convection, Conduction and Radiation. This method is the most accurate temperature calculation method available as it takes into account sea water velocities, insulation, sea temperatures, burial depth etc. For details on the equations, please refer to the PROSPER Manual.

To commence data entry for a new application, click All Edit. The program will then display all the input screens in sequence. To go back and edit one particular equipment item, click the button on the left of the appropriate item. Surface Equipment An example of the surface equipment screen is shown below:

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To calculate heat losses, additional data such as outside diameter, material type and insulation (if used) are required to be input. The surface equipment model can utilise the following equipment types: Line pipe Coated pipeline Flexible tubes user selected Choke Fittings To allow for pipe bends and fittings in general, the program contains a database with the K-values used to model the fitting of choice. The choke calculation handles both sub-critical and critical flow. The program will calculate the temperature drop across the choke. Descriptive labels for each element can be entered in the Label field if desired. Labels appear on reports and calculation screens. GAP User Guide

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Surface equipment geometry can be optionally entered as TVD of the upstream end of the pipe segment and length or as X, Y (from the manifold or the Xmas Tree) co-ordinate pairs. The Rate Multiplier column enables to simulate the pressure drop due to several wells being connected to a production manifold via a common surface flow line. The fluid velocity in the flowline is multiplied by the value entered - thereby increasing the frictional pressure losses. For most applications it should be left at its default value of 1. As an example, the pressure drop in a flowline connected to 3 identical wells could be modelled using a pipeline rate multiplier of 3. 2 parallel flowlines having identical dimensions can be modelled by entering the actual dimensions for one pipe and a pipeline rate multiplier of 0.5. It is also possible to vary the rate multiplier along the pipeline to simulate varying sections of dual pipelines for example. The editing buttons Cut, Copy, Paste, Insert and Delete operate on data records that have been selected by clicking on their row number button(s). All records can be simultaneously selected by clicking the All button. Use the Import button to import data from a wide variety of sources. Up to 200 pipe segments can be entered, enabling the user to model very long pipelines. Pipe insulation (e.g. concrete, foam or bitumen) can be modelled. To define the pipe insulation click the Enter button to display the following screen:

Select the required insulation type from the drop-down list and then enter the thickness. Enter the insulation beginning with the innermost layer. PROSPER uses the thermal properties in its database to calculate the thermal conductivity of the composite insulation. Click OK to return to the surface equipment screen. Different insulations can be entered for each section of the flowline as required. The calculated composite thermal conductivity is referenced to the pipe inside diameter. Pipes can be laid on the surface (burial depth = 0) or buried. The diagram below shows the 1990-2011 Petroleum Experts Limited

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burial depth geometry.

The burial depth is the distance between the soil surface and the bottom of the pipe (including insulation, if present). The pipe is partially buried if the burial depth < O.D. of the insulated pipe. Ensure that the flowline pipe geometry is consistent with the pipe burial depth. If necessary, insert another node and change the burial depth for e.g. the riser. The soil conductivity around buried surface pipes is taken from the Thermal Properties database for the shallowest rock type entered in the Lithology screen. In previous PROSPER releases, the soil conductivity was fixed at 3.5 W/ m/K.

Temperature Data Surface Environment data is required for the calculations of heat loss for surface flow lines and well risers. Data must be entered according to the screens shown below depending on whether prediction is being done offshore or on land (Specified from Options). Temperature Data Input (Off Shore):

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Temperature Data Input (On Land):

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Databases This optional feature is used to access the thermal properties databases for editing or addition of user-defined materials. Select Databases and click Edit and the following selection screen will be displayed:

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Enter appropriate values for the Conductivity of cement and casing. Depending on the selection, PROSPER expects input of thermal conductivity, emissivity, specific heat capacity, specific gravity or density. Check that the correct units are used before entering the thermal properties. Edited values remain in memory and become part of a particular well model file when the file is saved. To permanently save edited values or new user-defined entries for use in other projects, click the Save button to write them to the database. The Reset button is used to return all entries to their default values.

2.5.6.4.1.3 Improved Approximation

The advantage of using the Improved approximation option over rough approximation method is that although a heat transfer coefficient accounts for the heat losses from the inside of the pipe to the surroundings, the Joules-Thomson effect (cooling or heating of the fluid because of pressure drop in the pipe) is also accounted for. This can be of particular importance to gas pipelines, where the J-T effect can cause the formation of Hydrates in high pressure/low temperature situations. In addition to this, the user can enter more than one U-values for 1990-2011 Petroleum Experts Limited

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calculation of temperature drops (one for each segment of pipe). Equipment entry for the Improved Approximation temperature model varies little from the Rough Approximation option. Click on Equipment to display the following input screen:

To start data entry for a new application, click All Edit. The program will then display all the relevant input screens in sequence. If data has already been entered, clicking the Summary command button will display a summary of the current equipment. To go back and edit one particular equipment item, click on the button beside the appropriate item. Surface Equipment Surface Equipment requires the user to enter the temperature of the pipe surroundings and an overall heat transfer coefficient.

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The heat transfer coefficient can be specified for each pipe segment and should not be confused with the pipe thermal conductivity. The heat transfer coefficient accounts for the heat flow through the production tubing, annulus and insulation (if present) to the surroundings. Heat transfer by forced and free convection, conduction and radiation must all be accounted for in the value of the overall heat transfer coefficient. In PROSPER the overall heat transfer coefficient is referenced to the pipe inside diameter. 2.5.6.5 Gradient Calculation The PROSPER on line method also offers the user the facility of doing gradient calculations to see the pressure and temperature variations along a segment of pipe. This can be done through the “Calculate” button shown below:

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Results After a solve network or a material balance prediction calculation is done, the user can look into the results from the “Results” tab in the pipe summary screen:

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(Solve or Prediction):

Scrolling to the right will reveal a new button which is active now and will perform the gradient calculations along the pipe segment, thus showing the results not only up and down stream of the pipe but also along the pipe as well:

The gradient calculations will yield a number of different variables, like C factors, Flow regimes, holdup etc, which are essential in pipeline design.

2.5.6.6 Bottlenecks GAP can be used to detect "bottle necks" in the system: After a "Solve Network" is run, the bottle necked pipelines are turned red. GAP User Guide

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After a "Prediction" is run, a bottle neck flag is displayed in the pipelines prediction results, under the "Status" results column. Note that the option "Highlight Bottle Necked Pipes" has to be previously selected from the "View" menu. 2.5.6.7 Emulsion correction GAP includes a model that corrects the viscosity of the fluid in the presence of emulsions:

The emulsion correction will create a model for viscosity which will override the standard viscosity calculation based on the viscosity of the water and the oil in the pipe. It is based on the Woelflin correlation which can be matched to measured data. Selecting the “Emulsion” checkbox will lead to the activation of the Edit List button. GAP allows to create a different correction for each pipe in the system. Selecting the “Edit List” button, will prompt a table where the different models can be selected:

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The emulsion correction model requires the match parameters to be entered, or created based on the “Match” feature.

This will prompt the screen shown below:

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After entering the match data (the multiplier needs to be calculated based on the measurements of the fluid without and with emulsions), the “Match” button will create a model which can then be plotted:

The curve will look as shown below:

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The match performed with the parameters shown above will only change the first part of the curve (Woelflin model – parameters 2 and 3). For the viscosity correction applying to water cuts above the right plateau limit, an exponential decline is implemented that needs to be matched manually using parameters 4 and 5. Having done the match, the viscosity model can then be applied to one, some or all the pipelines in the system:

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2.5.6.8 Wax or Hydrate Risk GAP can also be used to determine if there is any risk or Wax or Hydrates being formed in the system. In order to perform this prediction, the Compositional Model from the Options Screen must be set to either Tracking or Fully Compositional. This is because the calculations require the fluid compositional details. If GAP does encounter an element where there is a potential for Wax or hydrate, a flag will be raised in the pipe element as shown in the figure below.

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The flag above refers to the Solve Network results. With regards to the prediction, the flag will be displayed in the Status column in the prediction results section.

2.5.7 Tanks

In GAP, Tanks (Reservoirs) are used to predict reservoir pressures and saturations for Prediction runs only. A Tank in GAP refers to a reservoir. It should not be confused with Stock Tank conditions. Tanks can be represented in GAP as A reservoir pressure decline curve MBAL Material Balance model file. Please remember to activate the prediction to “ON” from the Options/ Method screen:

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Within GAP three methods can be followed to model reservoirs: Material Balance Decline Curves

External Simulator

GAP can use MBAL Material Balance models to determine reservoir pressures and well GOR ’s and water cuts Decline Curves are entered as reservoir pressure as a function of cumulative production. The reservoir pressure decline therefore includes the effects of aquifer pressure support or fluid influx from adjacent reservoir units An external simulator (like REVEAL, Eclipse, Imex, MoReS, CHEARS, etc.) can be linked to wells. This can be achieved by linking GAP to the simulator using RESOLVE

Once a tank has been defined, production wells must be assigned to the tank. This can be done either by: Clicking the Tanks input tab from a Well data input screen, or From the Tank data entry screen (see below), or By dragging connections between wells and tanks, in a similar fashion to the creation of pipeline links. Wells can connect to more than one tank by entering appropriate allocation factors (for single-layer wells); Wells can connect to more than one tank by associating different tanks to different well inflow layers (for multi-layer wells); 1990-2011 Petroleum Experts Limited

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See below for more information on the assignment of tank connections. The tank data entry / results screen has three sections (as explained in the details of format for equipment, see above 149 ). These are itemised below: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data and the MBAL file that represents the reservoir (for MBAL prediction). It also allows the user to select which method to use for Prediction Includes tabbed screens for the following input fields: Well Connections (Valid/Invalid) Constraints (injection system only) (Present/None/Invalid) Production Data (decline curve prediction only) (Present/None/ Invalid) Injection Fluid (Injection source) Schedule (None/Some) Contains the following fields: Network Solver Results Prediction Results

2.5.7.1 Tank Summary Screen Double-click on a tank icon in the system window to obtain a tank summary screen.

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Main features Model

Type

PVT Model MBAL File

The user can select the method of prediction. There are three choices; Material Balance, Decline Curve, External Simulator (ref. previous paragraph 304 ) The fluid type will be automatically selected from the PVT description in the case of material balance prediction. The user can select the fluid type in case of Decline Curve predictions. Choices are: Oil Gas Retrograde Condensate In a material balance prediction, the MBAL model file decides the selection and this field is automatically populated This field displays the PVT modeling option used by the reservoir model. The options are: Black Oil, Fully Compositional and Tracking (Material Balance Prediction only) For a material balance tank, this gives the name of the MBAL file that contains the model for the tank. To select a new file, select the Browse button next to this field and choose a file from the selection dialog presented.

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Note that GAP must save all changes made in the data entry screen (for all items since the screen was opened) if one changes the tank file. A warning to this effect is produced when selecting a new file. Number of Tanks (Material Balance Prediction only) For a multi-tank, this displays the number of sub-tanks in the system Tank ID (Material Balance Prediction only) This displays the tank ID from the MBAL model file Start of GAP will look up the start of production from the MBAL tank and Production displays it here. In material balance mode only End of History Again this is used for Material Balance model only. GAP will display the end of history date in cases where the MBAL model contains historical data Original Oil The Original oil or gas in place is displayed and Gas in Place Run MBAL MBAL may be run with a DDE link by selecting this button. This is recommended in order to avoid building the tank models separately

Multiple tanks If a multi-tank MBAL file is loaded into this screen, the pie-slice icon that represents the separate tanks will be replaced by a number of icons, each corresponding to the tanks in the MBAL file. These may be treated individually in assigning well – tank connections. Transmissibility leaks between tanks are represented by lines joining tanks together.

2.5.7.2 Tank Input Data (Material Balance Tank)

2.5.7.2.1 Constraints This tab allows to enter constraints for the tank:

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2.5.7.2.2 Wells For a tank to be considered in the prediction calculations it must be connected to one or more wells. This can be achieved from this tab. Alternatively, similar connections can be established using the following methods: Connect the tanks from the wells screen by selecting the Tanks tab Drag a link between a well and a tank on the system window

In this screen, select wells from the ‘Not Connected’ list and click the Add button to connect them to the tank. Alternatively, disconnect wells by Removing them from the ‘Connected’ list: 1990-2011 Petroleum Experts Limited

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2.5.7.2.3 Injection This section is only used in cases where there is no associated injection system and allows to define the properties of the injection fluids, which are then used for pressure drop calculations. The screen has the following appearance:

Gas Injection Fluid

Edit List

Composition

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Select the injection source from the current list. The properties of the selected source will be displayed in the Source Statistics area below this. If compositional tracking option is selected, the statistics section has a composition button as well Invokes the gas injection source dialog (as accessed from the Options menu 76 item). Use this to update or add to the current source list Allows the viewing (read-only) of the composition corresponding to the selected source

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2.5.7.2.4 Tank Schedule This screen is similar to the schedule screens in other equipment nodes. The user can enter the dates and nature of events that need to be investigated.

2.5.7.2.5 Tank Results This screen is similar to the results screens in other equipment nodes.

2.5.7.3 Tank Input Data (Decline Curve Tank) When the Decline Curve option is chosen, similar input tabs than the one used for Material Balance tanks will be available, plus additional input data only relevant to this type of reservoir model, and that will be described below.

Type

This entry allows to define the main phase produced by the tank (Oil, Gas, Retrograde Condensate)

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2.5.7.3.1 Tank Production Data The reservoir pressure decline curves should be entered from the beginning of a Decline Curve Prediction run period; i.e. the reservoir pressure should be the current reservoir pressure. Cumulative production at the start of the prediction can be left at zero (predicted production will be relative to the current cumulative production for the tank). An example of a reservoir pressure decline curve (Production Data) input screen follows:

If one enters the current oil production it is possible to interpolate the data to estimate the tank pressure corresponding to that production by pressing the Calculate button. The reservoir pressure vs. cumulative production data can be entered by hand or pasted from the Windows clipboard.

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This feature allows to import and use as decline curve whatever result was previously calculated for the tank, for example using an MBAL model. This option can be used when one wants to substitute the reservoir model (for example, numerical simulation) with a quick decline curve to perform many scenarios that would require long run times if the simulator was used Interpolates the table to find the tank pressure corresponding to the value of Current Oil Production Plots the tank pressure against cumulative production, as entered in the table.

2.5.7.3.2 Compressibility This GAP option allows entering rock compressibility’s that vary with pressure.

There are two ways of defining the compressibility: on original volume and on tangent. On Original Volume

On Tangent

The Cf at pressure P and V is defined using the formula, Cf = - 1/Vi (V – Vi) / (P – Pi) Where Vi and Pi are the pore volume and pressure at initial conditions. This formulation means that the results are not dependant on the time steps selected The Cf at pressure P and V is defined using the formula: Cf = - 1/Vi (dV / dP)

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Where dV/dP is the derivative at pressure P. The program ALWAYS uses the original volume Cf so this column must be entered to make the dataset valid. However if the Use only has the Cf based on tangents, it is possible to enter this column instead and then use the Calculate button to calculate the Cf based on original volume. : . :

2.5.8 Flares and Vents NEW!!!

Flares and Vents are elements that can be used to account for emissions for reporting purposes. Flares and Vents act like sinks. Each flare or vent can be assigned a fix pressure or a fix rate. These are two typical applications of flares and vent.

Note that the two elements are interchangeable, as their difference is only visual. 2.5.8.1 Summary and Input These sections are the same as in Sinks 346 . 2.5.8.2 Results The Results tab is exactly the same as any other element. In the menu Prediction the results of the Flares and Vents are reported under Emissions. To access the Emissions select the menu Prediction / View Prediction Results System Emissions or, to plot, Plot Emissions Prediction Results. GAP User Guide

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2.5.9 Pumps

Pumps are defined by their Performance Data, which can come from a model or entered by the user depending of the selected pump type. Three Types of pumps are available: Performance Curves

Jet Pump

This is a table that relates head and power consumed to operating rate. The lookup table can also have speed and gas/liquid fraction as sensitivity variables. If desired, affinity laws can be used to scale the calculations for actual vs. design speed. The pump pressure calculations are based on an averaged rate through the pump; i.e. the volume changes as the pressure increases from inlet to outlet are taken into account. This averaged rate is then used as the input to the performance table to obtain a head, which is converted into a pressure using the average density of the fluid. Note that the calculations are repeated sequentially for the number of stages specified The model of a Jet pump can be used to account for the pump performance. The Jet pump can be selected from a list that mirrors 1990-2011 Petroleum Experts Limited

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Framo Pump

the database of pumps of PROSPER The model of a FRAMO Multiphase pump can be used to account for the pump performance. The pump can be selected from a list that mirrors the database of pumps of PROSPER

When defining a pump, it should be always placed between two joints, one at its suction and the other at its discharge. This is done, by dragging connections between pumps and joints with the Link icon selected. NOTE: the pump connections (represented by the white arrows) should be consistent with the actual flow direction:

Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the pump. See the following section for details Includes tabbed screens for the following input fields: Data (Valid/Invalid) Control (OK) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.9.1 Pump Summary Data Double click a pump icon to display the pump input summary screen:

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This shows the status of the various aspects of item data. These will be described next

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2.5.9.2 Pump Input Data

No of Stages

Use Affinity Laws

Actual Speed Design Speed Stage Data Edit TPD

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This is the number of stages in the pump. The stages are modelled as identical. Pre, post and inter stage separation can be set up via the Stage Data screen The Use Affinity Laws option must be selected when entering pump performance curve data. The pump model uses affinity laws to scale the calculations from design speed to actual speed. The pump speed values are entered by selecting the Control tab in the pump element input dialogue Current speed of operation of pump Design speed of operation of pump, to which the performance data refers Allows the specification of pre post and inter stage separation and cooling Allows the creation/editing of performance data for the pump. When creating the data from scratch, the after pressing Edit TPD, following screen will appear.

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On this screen, choose the variables for performance tables. These are: Operating rate Frequency Gas Fraction Rotational Speed One needs at least operating rate as a variable. Fill the data in the following table

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Delete TPD

Deletes the performance data entered for the pump. Once the performance data is deleted, the pump input sections are treated as new

2.5.9.3 Jet Pumps Option When the pump is defined as Jet Pump, the database with available jet pumps will become active as shown below:

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The user can then select the pump of choice, or edit the database to add more pumps if a given pump does not already exist:

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2.5.9.4 Pump Calculate Button On input data screen, there is a Calculate Button. This is the Pump Calculator, which can be used to calculate the outlet pressures, discharge temperature etc, for test data, given the pump performance tables entered.

One selected, the calculation screen will appear:

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The rate type list box can be used to select the desired input rate type. Pressing Calculate will perform the pump calculation for each line of data entered. The Initialise from solver results button can be used to load as input data the results of the latest Solve Network calculation. This allows to check the pump performance in the same conditions as the main Solve Network calculation. This screen can be extremely useful in matching the performance of the model to that of a real compressor. A typical set of performance curves for a centrifugal compressor consists of Inlet Rate Vs Head, Inlet Rate Vs Power and Inlet Rate Vs Dicharge Pressure. So, having entered the data, the user may enter various test points to check if for a given rate, inlet pressure and speed, the correct oulet pressure is displayed. If the pressure is not correct, then the polytropic efficiency of the machine can be changed to match real performance for example. Input Fields Table

Enter test rates and inlet conditions. The rate can be specified as a liquid rate, oil rate or gas rate, the type being chosen from the Rate Type combo box

Action Buttons Calculate Disable OK

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Cancel Help

Removes the dialogue Displays this screen

2.5.9.5 Pump Control The pump model in GAP is controllable in terms of speed of operation in order to optimise production. In order to activate the Control section, the user needs to provide information on how the pump will perform at different speeds. To this end, one can use either the affinity laws or use speed as one of the input variables.

The input screen will look like so:

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Speed Control The options are: Fixed

for no control case, the pump calculations are done with actual speed Actual Speed

Calculated

Speed to be used in fixed speed calculations

when the program calculates the speed of operation, which optimises production and obeys the total system constraints Actual Speed Optimised Speed Minimum Speed Maximum Speed

Speed to be used in fixed speed calculations (not optimised calculations) This will be selected by the optimiser of GAP when performing the calculations Operating range of the pump speed

2.5.9.6 Pump Schedule (ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the pumps can be scheduled to be masked/ unmasked during predictions. 1990-2011 Petroleum Experts Limited

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2.5.10 Compressors

Once a compressor has been defined, it is always placed between two joints, one at its suction and the other at its discharge. This is done, by dragging connections between compressor and joints with the Link icon selected. The three section buttons of the compressor have the following entries: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the compressor. The type of compressor is also selected in this section Includes tabbed screens for the following input fields: Data (Valid/Invalid) Control (OK) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

NOTE: The compressor connections (represented by the white arrows) should be consistent with the actual flow direction:

2.5.10.1 Compressor Summary Data Double click a compressor icon to display the compressor input screen:

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Main options Type

Data Summary Area

Select the type of Compressor here. The options available are: Performance Curves (Full model) Fixed dP Compressor Fixed Power Compressor Reciprocating This shows the status of the various aspects of item data

2.5.10.2 Input Data for Compressor (Full Model) This option is for modeling existing compressors with known performance curve data. Compressors have a similar performance data tables to pumps, although of course the gas rate is used. The rate at the inlet (calculated at that pressure and temperature) is used to look up the head and power. The head given by the table is interpreted as either polytropic head or isentropic head, 1990-2011 Petroleum Experts Limited

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depending on the check box setting in the input screen. The pressure calculations are performed by equating the head to that predicted from the isentropic or polytropic compression of a gas (see Gas Conditioning and Processing, by J. Campbell). The fundamental equation used to correlate head and inlet/outlet conditions in a compressor is given by:

Main input data No of Stages

Use Affinity Laws

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This is the number of stages in the compressor. The stages are modelled as identical. Pre, post and inter stage separation and inter-cooling for compressors can be set up via the Stage Data screen The Use Affinity Laws option must be selected when entering compressor performance curve data. The compressor model uses affinity laws to scale the calculations from design speed to actual speed. The compressor speed values are entered by selecting February, 2011

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the Control tab in the compressor element input dialogue. In certain cases, it is likely that the Performance Curves of the Compressor are defined at the ‘Design Speed’ only. If the objective is to perform the calculations at a speed which is different from the Design Speed, then the ‘Affinity Laws’ can be used. The affinity laws allow the performance curves to be scaled to a different speed. The affinity laws are also helpful when optimizing on the Compressor Speed, where these laws are used to define the performance of the compressor at speeds other than the Design Speed Use Overall Head (to fluid) and the Overall Efficiency are used to determine the power required by the machine based on the power given to Efficiency the fluid (calculated from the Head). If not selected, the user can directly enter the power consumed by the compressor and the program will calculate the efficiency Actual Speed Current speed of operation of pump/compressor Design Speed Design speed of operation of pump/compressor, to which the performance data refers Polytropic Efficiency When performing the calculations, the head required by GAP is the ‘Polytropic Head’. GAP will use the ‘Polytropic Efficiency’ to convert the ‘isentropic head’ into ‘polytropic head’. It is also possible to define the ‘Polytropic Efficiency Multiplier’ at various ‘Operating Rates’ to account for the variation of the polytropic coefficient with the rate flowing through the compressor. This Polytropic Efficiency Multiplier will scale the Polytropic Efficiency depending on the operating rates so that the performance of the compressor is captured accurately Use Polytropic Head When checked, the head in the performance data is taken to refer to polytropic head, otherwise the head is isentropic head. If the option ‘Use Polytropic Head’ is selected, then the Head defined in the performance curves will be treated as ‘Polytropic Head’. If the Isentropic Head is available, then this can be indicated by removing the stated option Edit TPD Allows the creation/editing of performance data for the compressor.When manually entering data, select Edit TPD, to access the following screen.

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Delete TPD

On this screen, choose the variables for performance tables. These are: Operating rate Frequency Gas Fraction Rotational Speed Deletes the performance data entered for the pump. Once the performance data is deleted, the pump input sections are treated as new

Performance Curve Input Data Compressor performance data can be entered in the following screen. The minimum amount of data necessary to describe the compressor performance is the operating rate relationship with head and power.

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The data required by performance curves are: curves of operating rate vs head to fluid and power to machine, where: Operating rate Head Power Polytropic Efficiency Multiplier

The gas rate flowing through the compressor, expressed at inlet conditions Measure of the energy (expressed in unit length) given to the fluid Power provided to the machine Multiplier is used to modify the polytropic efficiency with varying flow rate

The Head is the energy provided to the fluid and as such it is used to directly determine the dP provided by the compressor. The Power, instead, is an external power that is given to the machine. It is used only for reporting and for constraining the system and is not used to determine the compressor dP. Knowing the Head, it is possible to determine the power given to the fluid. The ratio of this power by the entered external Power is the compressor efficiency. If Overall Efficiency entry is enabled, in the place of the Power the user can enter the Overall Efficiency. The Overall Efficiency represents the ratio between the power to fluid (given by the Head) and the power to the machine, knowing the Head and the Overall Efficiency, one can determine the power required by the compressor. 1990-2011 Petroleum Experts Limited

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Surge/Choke Two additional variables enable to specify the compressor operational limits (i.e. stonewall and surge). Minimum Rate

Maximum Rate

(i.e. Surge) For every single compression stage, the minimum rate will be recirculated in the compressor: there will always be this rate flowing through the compressor (i.e. Stonewall) This maximum rate will be seen as a constraint applied on the compressor considered

Important: To have a good definition of the compressors performance, the curves defined in GAP should have atleast one point outside the operating range of the envelope. In other words, there must be at-least one point below the surge limit and one point above the choke limit. This allows for the operating conditions to be accounted for.

Example of Performance Curve An example of the operating curves is as shown in the following figure. This example has the performance curve at various rotational speeds.

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Compressor Performance Curves

Plot of Head Vs Operating Rate at various speeds

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Plot of Power Vs Operating Rate at various speeds

2.5.10.3 Input Data for Fixed dP Compressor This model will apply the specified pressure difference across the compressor. This model will also be an approximation to the actual performance of a compressor; as it will apply a constant dP independent of the flow rates flowing in the system. This compressor module should be used only for scoping studies, when the compressor has not been selected yet.

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Main Input data No of Stages

Polytropic Efficiency

Delta P

This is the number of stages in the compressor. The stages are modelled as identical. Pre, post and inter stage separation and inter-cooling for compressors can be set up via the Stage Data screen The polytropic efficiency is used for passing from isentropic coefficient (k) to polytropic coefficients (n). For recall, k is the ratio of specific heat, Cp/Cv. It is used for the discharge temperature calculation Pressure gain across each stage

2.5.10.4 Input Data for Fixed Power Compressor This model specifies a constant supply of Power to the compressor. GAP will use this power to calculate the Head developed by the compressor for the flow rate and thus calculate the dP across the compressor.

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Main Input Data No of Stages

Poly Efficiency

Power per Stage Overall Efficiency Surge Minimum Rate

This is the number of stages in the compressor. The stages are modelled as identical. Pre, post and inter stage separation and inter-cooling for compressors can be set up via the Stage Data screen The polytropic efficiency is used for passing from isentropic coefficient (k) to polytropic coefficients (n). For recall, k is the ratio of specific heat, Cp/Cv. It is used for the discharge temperature calculation The overall power input per stage of the compressor Overall efficiency, used to correct overall power input to actual input to the compressor This represents the minimum surge rate. If the rate entering the compressor decreases below the minimum surge rate, recirculation is activated, so that the actual flow through the compressor equals the minimum surge rate. The head is then calculated based on the minimum surge rate head

Efficiency

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This section enables to enter an overall efficiency multiplier as a function of the rate passing through the compressor. This enables to take into account the efficiency variation with rate

This compressor module should be used in the design phase (when the compressor has not been yet selected) or for scoping studies. A fixed power compressor by definition will give infinite head for low rates and may provide with inconsistent results. Because of this, a curve of efficiency vs rate should be entered to avoid infinite head. 2.5.10.5 Input Data for Reciprocating Compressor Four types of Reciprocating compressors can be modeled: Single Acting Head End Single Acting Crank End Tandem Double Acting The number of Stages is required, and for each stage the inputs are: Number of cylinders Stroke length Rod diameter Clearance (as a percentage)

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2.5.10.6 Compressor Control (Full Model Only) The compressor model in GAP is controllable in terms of speed of operation. The overall power constraint specified at field level is what determines the speed of the compressors. The input to the control section is

Speed Control Fixed

for no control case, the pump calculations are done with actual speed Actual Speed

Calculated

Speed to be used in fixed speed calculations

when the program calculates the speed of operation, which optimises production and obeys the total system constraints Actual Speed Optimised Speed Minimum Speed Maximum Speed

Speed to be used in fixed speed calculations (not optimised calculations) This will be selected by the optimiser of GAP when performing the calculations Operating range of the pump speed

2.5.10.7 Compressor Schedule (ONLY for Prediction) Like any other equipment in GAP, for models with prediction enabled, the compressor can be scheduled to be masked / unmasked during predictions. GAP User Guide

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2.5.10.8 Compressor Calculate Button Just like in the pump input data screen, on the Compressor input data screen, there is a Calculate Button. This is the Compressor Calculator, which can be used to calculate the outlet pressures, discharge temperature etc.

The rate type list box can be used to select the desired input rate type. Pressing Calculate will perform the compressor calculation for each line of data entered. The Initialise from solver results button can be used to load as input data the results of the latest Solve Network calculation. This allows to check the compressor performance in the same conditions as the main Solve Network calculation. NOTE: If the compressor is set to Controllable, then the solution speed from a solve network must also be updated in the main compressor input screen prior to using the performance calculator for results comparison, etc. When using the compressor performance calculator to review optimised compressor results for multistage reciprocating compressors, the optimised compressor speed MUST be entered in the compressor input screen prior to using the performance calculator utility. 2.5.10.9 Operating point in Plot NEW!!! The operating point can be displayed by accessing the TPD Input section after running a Solve Network calculation and plotting the compressor performance curve. GAP will display the operating point along with the compressor curve: 1990-2011 Petroleum Experts Limited

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2.5.10.10 Surge and Choke In GAP it is possible to define the Surge Rate (Minimum Rate) and Choke Rate (Maximum Rate) for the particular compressor. During the compressor calculations, if the compressor rate falls below the Surge Limit, then GAP will recycle the quantity of gas that is required. This means that if the Surge (Minimum) Limit is reached, the Head reported by GAP will correspond to the surge rates even though the actual throughput of gas (from the upstream elements) is less than the surge limit. If the quantity of Gas produced upstream of the compressor is greater than the Choke Limit, then GAP will increase the speed of the compressor so that the operating rate falls within the operating range of the compressor (This is only if the compressor speed is controllable.) 2.5.10.11 Efficiency vs rate This can be accessed by clicking in the Efficiency tab. This table allows to enter the variation of the overall efficiency of the fixed power compressor with the operating rates. The section is optional, however, when using Fixed Power compressor it is recommended to enter the curve of Efficiency with rate, in order to reduce the head given to the fluid and avoid inconsistent negative inlet pressures.

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2.5.11 Sources / Sink

When entering a source/sink element in the network, the following dialogue is displayed, to select either a Source or a Sink:

Sources/ Sinks are connected to the main surface network via a joint

2.5.11.1 Source Source is a point in a network, where a given rate of fluid (defined by the user or taken from a separator) is injected into the system, and to achieve that, the necessary pressure is applied: the required pressure at the source for the injection to be possible is calculated by GAP. The source element can be used in two different ways, depending on the objectives to achieve: Fixed rate / pressure sources

When the source is linked only to a joint, it injects in the system a fixed rate of a user-defined fluid. In this way inline injection or even contribution of fluid from a nearby field, for example, can be modelled.

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Separator oil/gas/ /water line

Sources that are connected to separators and handle a separated stream ( gas, oil, water or a mixture thereof). When a source is linked directly to a separator (fixed pressure or inline separator) the source can be used to pick on of the phases (oil, gas or water) and send it to a downstream network. In order to inject that amount of fluid, it will apply the necessary pressure, allowing in this way to model the outlet of a pump or of a compressor. This is particularly useful in design phase, to determine the duty of pumps and compressors.

To define which phase to pick up through the source, access the source Summary screen and select the Type as shown below:

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2.5.11.1.1 Source Data Entry The three section buttons of the source have the following entries: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the source. The type of source is also selected in this section Includes tabbed screens for the following input fields: Fluid (Valid/Invalid) Fixed Rate(Valid/Invalid) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.11.1.1.1 Source Summary Data

This following screen is the source summary data screen.

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Main Options Type

Depends on Pressure constrained

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Here the type of source is selected. The options depend on whether or not the source is connected to a separator. Standalone If the source is independent source, the sources options are: Fixed Rate Fixed Pressure Sources For sources connected to separators, the connected options are: to Separated gas separators Separated water Separated Oil Indicates the separator directly connected to the source If ticked Yes the source will have the same pressure as the connected separator, otherwise (recommended in most cases) the source will apply the required pressure to transfer the fluid to a February, 2011

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downstream network, modeling in this way the effect of a compressor of a pump This shows the status of the various aspects of item data

The separated oil stream, contains the remainder of the fluid inlet stream after the user defined gas % and water % are separated in the separator. For defining the fixed rate and the fluid, we go to the following screen from the summary area and define the inlet fluid rate and the temperature. 2.5.11.1.1.2 Source Data Input

From the summary area the fluid source is defined in the following screen:

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Select from the drop down list the gas / water injection source to be applied to the system derived from this manifold. When the injection system is associated with a production system, the source must be chosen from the list maintained with the production system. Otherwise the user may select the source from the injection system list. The properties of the source selected here are displayed in the ‘statistics’ area at the bottom of the screen. Edit List Fluid Properties

This button allows to edit the gas / water / steam injection source list This can be used to view the details of the properties of the injection fluid. In case one of the compositional options is enabled, the Injection Fluids section will have a ‘composition’ button as well. Clicking this will display the composition associated with the injected fluid that will be used in the calculations

2.5.11.1.1.3 Source Schedule (ONLY for Prediction)

For Prediction runs, like any other equipment, sources can be scheduled from this screen.

2.5.11.1.1.4 Steam Stream

Refer to the section "Equipment Data | Separator (Production / Injection ) | Injection Source Details 237 | Steam Stream" 2.5.11.2 Sink Sink is a point in a network, where a given rate of a fluid (a user input) is removed from the system at the connecting joint. Sinks need to be linked to a joint.

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Short label used to distinguish equipments on the system drawing. Up to 12 characters are allowed Takes to the data entry screen for the source Takes to the main GAP drawing

2.5.11.2.1 Sink Data Entry The three section buttons of the sink have the following entries: Summary Screen Input Screen Results Screen

This screen gives the status of various aspects of the input data for the sink Includes tabbed screens for the following input fields: Fixed Rate(Valid/Invalid) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.11.2.2 Sink Summary Data This following screen allows the data entry for the sinks

Type Data Summary Area

Here we select the type of the sink. Only one option is available: Fixed Rate This shows the status of the various aspects of input datasets

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2.5.11.2.3 Sink Input Data

On the rate data entry screen, the rate type is defined. The options are: Water Gas Oil Liquid

2.5.11.2.3.1 Sink Schedule (ONLY for Prediction)

For Prediction runs, like any other equipment, sinks can be scheduled from the schedule screen.

2.5.12 Inline Elements

This is generic piece of equipment that can be placed anywhere in the surface network between two joints. When an inline element icon is placed in the main window, the user will get the following dialogue, allowing the selection of various types of inline elements.

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The options available are: Inline Gate Valve Inline Check Valve Inline Separation Inline Choke Inline Injection Inline General (up to now known as “Inline Programmable”) Inline Elements are placed in the main surface network between two joints. Label Edit Cancel

Short label used to distinguish equipments on the system drawing. Up to 12 characters are allowed Takes to the data entry screen for the element Reverts back to the main GAP screen

2.5.12.1 Inline Gate Valve The Inline Gate Valve is an on / off type of valve. This element should be placed in network, if we want to control the start / stop of the flow of fluids through certain parts in the network. The three section buttons for data input of the Inline Gate valve have the following entries: Summary Screen

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Input Screen

Results Screen

This section contains an entry screen for the Schedule (ONLY FOR PREDICTION CASES) Like any other equipment in GAP, for models with prediction enabled, the gate valves can be scheduled to be masked / unmasked or bypassed / unbypassed during predictions Contains the following fields: Network Solver Results Prediction Results

2.5.12.1.1 Inline gate Valve Data Summary Screen

Main options Type

Status

Data Summary Area

Here we select the type of the element. Two options are available: Gate Valve Check Valve When selecting the type gate valve, two options are available: Open Close This shows the status of the various aspects of input datasets

2.5.12.1.2 Input Data / Schedule ( ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the gate valves can be scheduled to be masked/ unmasked during predictions.

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2.5.12.2 Inline Check Valve The Inline Check Valve should be placed in a surface network, if the objective is to physically stop the flow reversal in a segment of the surface lines. The three section buttons for data input of the Inline check valve have the following entries: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the Inline check Valve. The type of Inline check is also selected in this section This section contains an entry screen for the Schedule (ONLY FOR PREDICTION CASES) Like any other equipment in GAP, for models with prediction enabled, the check valves can be scheduled to be masked / unmasked or bypassed / unbypassed during predictions Contains the following fields: Network Solver Results Prediction Results

2.5.12.2.1 Inline Check Valve Data Summary Screen The Inline Check valve has the following data entry screen:

Type

Data Summary

Here we select the type of the element. Two options are available: Check Valve Gate Valve This shows the status of the various aspects of input datasets

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Area

2.5.12.2.2 Input Data / Schedule ( ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the check valves can be scheduled to be masked/ unmasked during predictions.

2.5.12.3 Inline Separation If there is a separation within the network, where the pressure values are not fixed like a separator, but floating, the inline separation element can be used. The three section buttons of the inline separation have the following entries: Summary Screen Input Screen Results Screen

This screen gives the status of various aspects of the input data for the inline separation. The type of inline separation is also selected in this section. Includes tabbed screens for the following input fields: Separation (OK/Invalid) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.12.3.1 Inline Separation Data Summary Screen The Inline Separation has the following data entry screen:

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Here we select the format in which inline separation variables are defined. The following options are available: % Separation Fixed Q Removal This shows the status of the various aspects of item data

2.5.12.3.2 Inline Separation Data Input Screen

The separated oil stream, contains the remainder of the fluid inlet stream after the user defined gas % and water % are separated in the separator. If Fixed Q Removals had been chosen in Type, The separation parameters are rates rather than % values.

2.5.12.3.3 Input Data / Schedule (ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the inline separators can be scheduled to be masked/ unmasked during predictions.

2.5.12.4 Inline Choke If there is fixed / controllable choke in the pipeline network, this element can be used.

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The choke model implemented in GAP is based on the Perkins choke model. The three section buttons of the inline choke have the following entries: Summary Screen Input Screen Results Screen

This screen gives the status of various aspects of the input data for the inline choke Includes tabbed screens for the following input fields: dP Control (OK) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.12.4.1 Inline Choke Data Summary Screen The Inline Choke has the following data entry screen:

Data Summary Area

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This shows the status of the various aspects of item data

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2.5.12.4.2 Inline Choke dP Control

The options for entering the pressure drop are: None Fixed dP Fixed Choke Diameter Calculated

No pressure drop across choke considered A fixed pressure loss equal to value entered is taken for all rates the choke size is considered being constant The drop calculated by GAP

The option Calculated determines the best setting for the choke in order to optimise production and satisfy various constraints specified in the system.

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Note that there is a choke calculator online that allow to estimate the choke size for given inlet and outlet conditions:

The plot button allows displaying the performance curve of the choke with the current operating point. The discharge coefficient relates the actual flow to the ideal frictionless flow. By default the discharge coefficient is 1, which means that the Perkins model is used as such. If choke measurements are available, it is possible to tune this parameter so that the choke model reproduces them. This feature makes the choke model in GAP general and customizable.

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2.5.12.4.3 Input Data / Schedule (ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the inline chokes can be scheduled to be masked/ unmasked during predictions.

2.5.12.5 Inline Injection If there is injection of a particular within the network, this option may be used. Examples are: riser lift gas injection, inhibitor injection in surface lines, etc. The three section buttons of the inline choke have the following entries: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the inline choke Includes tabbed screens for the following input fields: Fluid (OK / Invalid) Injection Rate (OK / Invalid) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.12.5.1 Inline Injection Data Summary Screen The Inline Injection has the following data entry screen:

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Data Summary Area

This shows the status of the various aspects of item data

2.5.12.5.2 Inline Injection Data Input Screen For defining the fixed rate and the fluid, we go to the following screen from the summary area and define the inlet fluid rate and the temperature.

2.5.12.5.2.1 Defining the Injection Rate

In this screen, we define the rate, inlet temperature and rate type of the injection fluid.

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Rate Temperature

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Two options are available: Fixed A fixed rate is defined which is injected into the network at that point Optimised GAP will inject a rate that minimises the pressure loss in the network downstream of the injection point in order to maximise production Define the rate of injection or maximum rate of injection Define the injection fluid temperature

The optimised method can be used to model RISER LIFT scenarios

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2.5.12.5.2.2 Defining the Injection Fluid PVT

Select from the drop down list the gas / water injection source that one would like to be applied to the system derived from this manifold. When the injection system is associated with a production system, the source must be chosen from the list maintained with the production system. Otherwise the user may select the source from the injection system list. The properties of the source that is selected here are displayed in the ‘statistics’ area at the bottom of the screen. Edit List Fluid Properties

This button allows to edit the gas / water / steam injection source list This can be used to view the details of the properties of the injection fluid. In case one of the compositional options is enabled, the Injection Fluids section will have a ‘composition’ button as well. Clicking this will display the composition associated with the injected fluid that will be used in the calculations

2.5.12.5.3 Schedule (ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the inline injection elements can be scheduled to be masked/ unmasked during predictions.

2.5.12.6 Inline General The inline General (Programmable) element can be used to define a variety of speciality equipment parts/ like pressure loss elements, control valves, heat exchangers etc in the surface network through an internal script.

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The three section buttons of this element have the following entries: Summary Screen Input Screen

Results Screen

This screen gives the status of various aspects of the input data for the inline General element Includes tabbed screens for the following input fields: Script (OK) Variables (None/Some) Schedule (Prediction Only) Contains the following fields: Network Solver Results Prediction Results

2.5.12.6.1 Notes on Inline General Elements Inline programmable objects are objects whose behaviour is controlled by a program script rather than a particular physical model (e.g. pipe). These can therefore be used to create a user defined equipment type. The syntax used is similar to the C programming language, and the variables considered can be accessed using strings similar to the one used in OPENSERVER. It is important to notice than when using an inline element, only the current model (i.e. Production or Injection) can be accessed. The inline script cannot access the injection model when the inline element is located in the production model. The following example shows the basic structure of a program script. The example applies a fixed pressure drop over the object. Example: Apply a fixed pressure drop of 50 psi over the inline element

DeltaPressure = 50.0; PRESOUT = PRESIN - DeltaPressure; if ( PRESOUT < DeltaPressure ) PRESOUT = DeltaPressure;

Each line must be terminated by a semi colon. Local variables 362 (such as DeltaPressure) do not need to be declared. One can access various variables defined in GAP that correspond to the inlet and outlet conditions of the inline programmable object, as well as during the solver to most of the variables the solver is using to calculate. In the above example, PRESOUT is the outlet pressure and PRESIN is the inlet pressure. These values can be changed by the script. The Inline General Element uses Field Units in all calculations. NOTE: All calculated Fluid Density values are returned in SI Units i.e., g/cc. 1990-2011 Petroleum Experts Limited

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2.5.12.6.2 Inline General Input Data (Script) Screen The following screen is used to write the script for the element or associate the element with a script file *.gsc by using the browse button at the top of the screen.

2.5.12.6.3 Inline General Script Variables There are three different classes of variables that can be defined and used in the inline general element script: Local Temporary These variables are defined by the user within the script to for instance proceed to calculations internal to the script. Variables The values associated to these variables are lost at the end of the script Temporary These variables are defined using the TEMPVAR[0…10] or ITEMPVAR[0…10] keywords. See section below 366 Variables The values associated to these variables are initialised to 0 at the beginning of the solver calculation. The values associated to these variables can be kept throughout the solver calculation process (i.e. they will be kept throughout the solver calculation iterations) but will be lost at the end of the solver calculation Permanent These variables are defined within the inline general script and their value can then be accessed and modified within the Variables Variable screen of the inline general element. These variables will be kept throughout the entire calculation

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Important Note on Permanent Variables These variables are not re-initialized when the run ends or is cancelled, therefore it is recommended to use these variables only for fixed values such as constraint for instance, and to avoid having them modified during the calculation. These variables should only be used to define a state (i.e. such as open, closed) or a parameter (i.e. such as frequency, power, efficiency, delta P) that will be used by the associated script to model the behaviour of this inline element. These permanent variables must not be used to store temporary values during a solver or prediction run. This will severely slow down the solver and may cause repeatability issues. At the end of the solver, these variables are left with the value stored in them on the last iteration of the solver or when the Cancel button was clicked. Instead, the TEMPVAR and ITEMPVAR arrays need to be used to store temporary values. The user defines the name of each variable. Name of existing or predefined script variables are not allowed. Therefore, any name starting with VAR should be adequate. There is no limitation to the number of user defined variables. These variables will be accessible through OPENSERVER, and OPENSERVER string can be found using the Ctrl + Right Click facility.

the

2.5.12.6.4 Schedule (ONLY for prediction) Like any other equipment in GAP, for models with prediction enabled, the inline general elements can be scheduled to be masked / unmasked during predictions.

2.5.12.6.5 Inline Element Variables This section lists the variables that can be changed or accessed in the script and their associated units. Five stream arrays exist in an inline element: IN[...]

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OUT[...] SEPGAS[...]

SEPOIL[...]

SEPWAT[...]

Outlet stream This is a stream (called gas but not necessary being gas) that is separated and sent to a gas source connected to the inline general element This is a stream (called oil but not necessary being oil) that is separated and sent to an oil source connected to the inline general element This is a stream (called water but not necessary being water) that is separated and sent to a water source connected to the inline general element

The following keywords can be used to access the array values : CO2 CO2FREE DILSG GGHV GNHV H2S H2SFREE N2 N2FREE PRES PWFSG QDIL QGAS QGFREE QMOLE QOIL QPWF QPWFU QWAT REVENUE SGG SGGFREE SOG TEMP WENT

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CO2 mole percent (mole percent) injected gas CO2 mole percent (mole percent) diluent specific gravity (sp. grav) gas gross heating value (MMBTU/d) gas net heating value (MMBTU/d) H2S mole percent (mole percent) gaslift gas H2S mole percent (mole percent) N2 mole percent (mole percent) injected gas N2 mole percent (mole percent) pressure (psig) power fluid specific gravity (sp. grav) diluent rate (STB/day) gas rate (MMscf/day) - black oil model only, otherwise use QMOLE injected gas rate (MMscf/day) - black oil model only, otherwise use QMOLE mole rate (mol/lbm/sec) - compositional model only oil rate (STB/day) - black oil model only, otherwise use QMOLE power fluid rate (STB/day) power fluid rate used (STB/day) water rate (STB/day) revenue/cost of fluids flowing through ( 6.0 ) { PRESOUT = PRESIN – 50.0; QWATOUT = QWATOUT * 0.75; } if ( QGASIN > 6.0 ) { dP = 50.0; } else { dP = 100.0; } PRESOUT = PRESIN - dP; if ( PRESOUT < dP ) PRESOUT = dP; i = 0; dP = 0.0; while ( i < 10 ) { dP = dP + 10.0; i = i + 1; } PRESOUT = PRESIN - dP; i = 0; dP = 0.0; do { dP = dP + 10.0; i = i + 1; } while ( i < 20 ); PRESOUT = PRESIN - dP; dP = 0.0; for ( i = 0; i < 21; i++ ) { dP = dP + 10.0; } PRESOUT = PRESIN - dP;

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2.5.12.6.16 Example Script Calculating the number of days since 1900. The following script fragment will calculate the number of days since 1900 for a calendar date. // Date to convert is 14th September 1996. Year = 1996; Month = 9; Day = 14; // Check if a leap year - the rules are:// If divisible by 400 then it is a leap year // If not divisible by 400 BUT divisible by 100 then it is NOT a leap year // If not divisible by 100 but divisible by 4 then it is a leap year. LeapYear = 0; if ( Year % 400 == 0 ) LeapYear = 1; else if ( Year % 100 == 0 ) LeapYear = 0; else if ( Year % 4 == 0 ) LeapYear = 1; Year = Year - 1900; NumDays = Year*365; // Add extra days for leap years NumDays = NumDays + floor((Year+3)/4); // Don't count the days for the current month Month = Month - 1; // Add up days for the months in the current year while ( Month > 0 ) { if ( Month == 2 ) { if ( LeapYear == 1 ) NumDays = NumDays + 29; else NumDays = NumDays + 28; } else if ( Month == 4 || Month == 6 || Month == 9 || Month == 11 ) { NumDays = NumDays + 30; 1990-2011 Petroleum Experts Limited

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} else { NumDays = NumDays + 31; } Month = Month - 1; } NumDays = NumDays + Day;

2.5.13 Inflow Icon

This element allows to decompose the wellbore into sections and model multilateral and complicated down hole geometry in GAP. The inflow data entry is split into three sections as described below. Summary Screen Input Screen Results Screen

This screen gives the status of the input inflow data and allows the type of well (producer or injector) and the location of an appropriate PROSPER file to be defined This screen allows the input data to be entered. The options in this section are the same as the IPR description discussed in IPR section 167 Contains the following fields: Network Solver Results Prediction Results

2.5.13.1 Inflow Summary Screen The inflow summary screen is shown below.

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The browse button is used to select the location of a PROSPER file that contains the IPR description. The file defined here can be used to import the IPR information into GAP as outlined in th section concerning IPR Generation 390

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2.5.13.2 Input Refer to IPR section 167 for further details.

2.5.14 Grouping

The grouping option allows collections of equipment to be controlled from one icon. The Group summary screen is divided into three sections. 1990-2011 Petroleum Experts Limited

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Summary Screen Input Screen Results Screen

Allows navigation to the constraints and grouping input screens. If under the |Options |Method screen the prediction option is set to on this screen will also allow navigation to the scheduling screen Allows values to be entered to constrain and schedule the group Contains the following fields: Network Solver Results Prediction Results

In order to create a group of nodes firstly add a group to the current system screen. To associate a node with a group there are two options: 1. Press the control key and the left mouse button over the node and move the mouse cursor until it is over the group. Now release the left mouse button. 2. Connect the well to the group using the Add Link/Pipe tool Three wells associated with a particular “Group1” are shown below.

2.5.14.1 Grouping Data Entry

2.5.14.1.1 Constraints When constraints are entered into the constraints input screen, the values entered represent an overall constraint that the sum the values for the nodes in the group cannot exceed. If the GAP User Guide

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maximum gas production rate for group 1 is set to 5MMscf/day, then the overall quantity of gas produced from wells “W1”, “W2” and “W3” will be constrained so as not to exceed this quantity.

For systems containing multiple compressors, the Group Constraints section will show an additional constraint option for Maximum Power. This feature has been designed to be used to manage the maximum compressor power distribution between two (or more) independent networks. It is not designed to be used for single network systems. A total compressor maximum power constraint for single network systems can be imposed on any downstream node (or separator) from the last compressor described in the given system. 2.5.14.1.2 Schedule The Group scheduling screen is shown below. The event type column allows a selection to be made between mask, unmask and change constraint. The mask and unmask commands allow all of the nodes in the group to be masked or unmasked. If the change constraint option is selected then the constraint type and a new value for the constraint need to be defined in the blue columns.

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2.5.14.1.3 Grouping The screen that is displayed when the grouping tab is clicked is shown below:

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Each group can belong to other groups. This field highlights the groups this group belongs to This field highlights the groups this group does not belong to Elements of the network that belong to the group

The Add and Remove buttons allow pieces of equipment to be added to or removed from the current group. Selection of elements belonging to a group It is possible to select al the members belonging to the group by right-clicking on the group (or using the menu Edit/Selected Groups) and selecting Show Members as Selected:

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2.5.15 Flowsheets

Flowsheets can be created to facilitate the visualization of big GAP models. It is possible to embed parts of the GAP model to a smaller subscreen Considering the GAP model below, a worksheet can be created to group all the wells flowing from the manifold WH1:

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The objective for this small example will be to copy the elements of RES1 production side to a separate flowsheet. Hence the elements that will be placed are Res1, Well1, Well1_ESP, Well1_GL, WH1. Step 1: Copy the items

Copy the items from by using the "Select" pointer from the

main tool bar . Once the select pointer has been selected, elements can be marked for copying using a left-mouse click. Once the desired model elements have been selected, simply right-click in the main GAP screen and select "Extract to GAP Partial FIle (*.gpp") from the pop-up menu. This will save a .gpp file to a relevant directory. To insert the previously copied sub network into the flowsheet, enter the flowsheet and right-click and select "Insert GAP Partial File" from the pop-up menu Step 2: Create the Create a flowsheet in the main production flowsheet, using Flowsheet the "Flowsheet" icon from the main menu bar. Step 3: Paste the In the new flowsheet, right clicking and select the option elements in the 'Insert Gap Partial File'. flowsheet Point it to the .gpp file that was created in step 1. This will paste all the five elements inside the flowsheet. Clicking on Window Tile Vertically will display both the Main network and the flowsheet side by side.

Step 4: Create the The next step will be to create the flowsheet port. 'Flowsheet Port' The flowsheet port is the link between the flowsheet elements and the main network. In the above example this link will be the

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joint 'WH1'. To create the flowsheet port, double click on the WH1 element inside the flowsheet (and not in the main network), and in the summary section, there is an option that says 'Flowsheet Port'. Select the Radio button. Alternatively, it is also possible to just right click on the WH1 (inside the flowsheet and not in the 'Main Network') This will publish the WH1 element inside the main network as shown in the figure below.

Step 5: Create the The worksheet port created on the main worksheet can now link between the be linked to the rest of the network. Flowsheet Port Since the objective is to link up the WH1 to the Manifold, a link and the other elements in the will be created between the flowsheet port and the joint called 'Manifold'. This will of course be an empty link between the two main network. nodes. The main network will look something like this.

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Step 6: Copy the Since the pipeline definition is already present in the link contents of the between WH1 (old) and Manifold, this needs to be copied pipeline across to across to the newly created link between the WH1 (new) and the newly created the Manifold. The easiest way to do this is to press down the CTRL button on pipe. the keyboard, left click on the existing pipe and drag - drop on the newly created link. The screen after the drag and drop will look like this.

Step 7: Delete the duplicated Network elements.

The items duplicated can be deleted from the main flowsheet The GAP model after the deletion will look like this.

The initial model and this model above are exactly equivalent. It might be possible that an item remains duplicated (such as a common joint), and therefore the icon will turn "invalid", as GAP detects twice the same label within the same instance. Double clicking on the Flowsheet will open up a new window containing the section of network under the Flowsheet. To Enter the Flowsheet Summary/Input/Results Screen, right click on the Flowsheet and select Edit. 1990-2011 Petroleum Experts Limited

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2.5.15.1 Summary, Input, Results These sections are accessed by right-clicking on the Flowsheet element. The Summary screen is just any other element (ref. Summary 152 section). In the Input section contains the Schedule, which allows to set events on the Flowsheet along a Prediction.

2.5.16 Notes on Constraints When setting up the model, it is recommended to start with the minimum necessary number of Constraints. In this way the user has the possibility to validate that the model performs as it is supposed to. After that, the number of Constraints can be increases, if necessary. GAP provides with a physical model of the whole production/injection system. This means that any constraint imposed in the system should reflect the physical reality of the field. For example, if a well at its maximum production cannot produce more than 1000 STB/day oil rate, it would not have sense to set up a minimum production constraint of 2000 STB/day, as this would be impossible to achieve. Based on these considerations, it is recommended not to use minimum constraints during a prediction run. In the case where minimum constraints cannot be physically honoured (because the system not necessarily can deliver the minimum liquid rate as the reservoir depletes, for example), the optimiser will try to honour an infeasible situation. This may provide unreliable results for the whole system. If the objective is to shut down the well if this cannot produce a minimum amount, this can be achieved by setting up an Abandonment Constraint of minimum rate in the Abandonment section: as soon as the well production decreases below the set minimum abandonment constraint, the well will be closed.

2.6 VLP/IPR Generation This chapter describes the following procedures: Batch mode transfer of well inflow performance relations from PROSPER Batch mode generation of well vertical lift performance curves using PROSPER Batch mode generation of pipe VLPs How to import externally generated well and pipe VLPs into GAP GAP User Guide

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How externally generated well IPRs can be imported into GAP NOTE: For being able to generate IPRs or VLPs in batch mode, GAP needs to know the path of the PROSPER file associated to each specific GAP well model. Therefore a PROSPER file needs to be associated to the well instance in GAP.

2.6.1 A well model in GAP A well model is essentially a mathematical representation of a real well. It needs to be able to represent past performance of the well (Flowrates, Water Cut, GOR etc) in order for the engineer to have confidence in prediction results from the model. The most common results a well model can provide are rates for a given well head pressure, GOR and WC. This is done on the basis of VLP/IPR plots (Bottom Hole Pressure Vs Rate), as shown below:

The intersection between the VLP and the IPR gives the rate and bottom hole pressure under the given conditions. In order to create this model, IPRs and VLPs need to be created for all the conditions the well will encounter during its life. Together the IPR model and the VLP set constitute a well model:

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2.6.1.1 IPR Inflow performance relationships are transferred from PROSPER. GAP has the PI and Vogel relationship (for Oil wells) built into it and therefore the choice of model used in PROSPER to generate the IPR is irrelevant. GAP will find an equivalent PI that can match the curve from PROSPER and this will be used to perform the well calculations. The data entered in the IPR section can be verified by accessing the well IPR Input 167 section. 2.6.1.2 VLP Lift Curves are generated by the PROSPER well file. The procedure will be outlined in the following sections 402 . In order to inspect the VLP curves in the GAP well model, click on "Inspect" from the well VLP section (ref. VLP Inspection 193 section) 2.6.1.3 Importance of VLP Data Ranges In order to enable GAP to calculate production rates and optimise, it is essential that the VLP/ IPR data represent the well performance accurately. Before running any calculation it is recommended to verify the quality and accuracy of the calculated VLP and IPR curves

2.6.2 Batch Generation of IPR’s 2.6.2.1 Single layer wells The following description assumes that a PROSPER model which includes an IPR has already been built for each well. It is first necessary to tell GAP the location of the PROSPER files that describe each well. The method of doing this is summarized below: 1. Open the well summary screen by double clicking on the well icon. A well summary screen is shown in below:

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2. Click on the summary button in the bottom left hand corner of this window. 3. Click on the browse button to open a file selection dialogue box. From this dialogue box select the appropriate PROSPER file for the well. Repeat this process for each of the wells that require IPR generation. Note that this is an operation that is performed just once, when the model is built. Now that the appropriate PROSPER files have been specified for each well Click "Generate Generate Well IPR’s with PROSPER" from the main menu bar. If some wells have been selected this window should appear:

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The user can then select from the list of wells selected the wells to generate the IPR for. If no wells have been selected a message warning the user of this is first displayed.

If the “All” button is selected, GAP will automatically select all the wells in the system and open the screen shown before where all the wells can be selected or de-selected individually. The button "Generate" is eventually used to transfer in batch mode the IPRs from the PROSPER files to the GAP well models. The result is that the IPR is imported in the well IPR section:

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In the case of multilayer wells (wells where multiple IPR have been added in the IPR Layer section), clicking the Generate button GAP will display the Enter Layer Indices screen in the case of multilayer wells

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The Enter Layers Indices screen is used to select which layer the IPR data read from prosper will be applied to. In the case of PROSPER multi-layer IPR model wells it should be noted that the total IPR (of whatever model chosen in PROSPER) is transferred to GAP. Therefore if transfer data to multi-layer models is selected, a target layer in each case must be especified to link the IPR data to be written to. If multi-layer wells had been selected, these will be listed in a screen after the Generate had been pressed. From the appropriate list boxes the target layer for the data in each case can be seected. Click |OK to start PROSPER. Each well’s input (.SIN) file will be opened in sequence and the IPR data will be automatically read into GAP. GAP uses its current type of IPR model for the well regardless of the IPR model used in the generation by PROSPER. This means that Oil IPR’s are always modeled with a PI and Vogel correction, while Gas/Condensate IPR’s are always Forcheimer or C and n. GAP takes the reservoir pressure and PVT information from PROSPER along with three IPR data points. These points become the Match points in the GAP model, and GAP fits its IPR coefficients to these points. 2.6.2.2 Multilayer wells The two following cases will be addressed. a) Generating multiple IPRs in GAP when having different PROSPER files for each layer. GAP User Guide

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b) Importing multiple IPRs in GAP when having one single PROSPER file with a Multilayer IPR model. The following example considers a Multilayer gas well: Case a In this case it is assumed that each IPR layer in GAP corresponds to one PROSPER file (***. out) containing a single layer IPR model (Jones, Forcheimer, etc.). The objective is to import into GAP each IPR . The following figure illustrates the objective.

This can be achieved by first associating each layer to the correspondent PROSPER model and then generating the IPRs in batch model in GAP. This allows to import all the IPRs in one go. This is the process to follow: Associate in GAP each layer to each PROSPER model. This can be achieved by accessing the IPR Layer section and selecting Browse to recall the correspondent PROSPER file. This is shown below:

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Repeat that for all the Layers. To skip through the layers select the layer number from the top-right corner selection dialog. Import the IPRs accessing from the main program menu Generate/Generate well IPRs with PROSPER The IPRs will be imported all in GAP Case b In this case it is assumed that there is one single PROSPER file (***.out) with a multilayer IPR model, and we need to import each layer IPR in GAP assigning each IPR to different well-tank connections in GAP. The following figure illustrates the objective.

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This is the process to follow: Select the Multilayer PROSPER model in the GAP Well Input Screen (Summary section) as shown below:

Open the PROSPER model (click on "Run PROSPER", as shown above). Access the IPR section (System | Inflow Performance Relation )

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Click on Input Data, and deselect all the layers but the first one. This can be done by selecting the blank option in the IPR type pop-down menu (the other layers data will be kept stored and will be recall every time the IPR type is restored).

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Click "Calculate" to calculate the IPR, then "Done" to exit the IPR screen. Save the PROSPER file, and return to GAP by clicking "GAP" from the main PROSPER menu 1990-2011 Petroleum Experts Limited

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bar. Once in GAP, Click on "Generate | Generate well IPRs with PROSPER" from the main GAP menu bar. Click "All" and select the well for which to generate the IPR. Click on "Generate"; It will be asked to select the Tank model (in brackets) to which the IPR will be assigned. Select the Tank model using the drop down menu illustrated below and click "Ok".

The IPR will be generated for this only specific layer. In order to generate the IPR for the Layer 2, open the PROSPER file again. In the PROSPER IPR section, deselect the layer 1 and select the layer 2 as shown below:

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The previous steps are then repeated (PROSPER file saved, IPR generated in GAP for the second layer, etc...) for all the layers. The different layers' IPRs can then be inspected, using the drop down menu in the GAP well model, as shown below:

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2.6.3 Batch Generation of Well and Pipe VLPs

2.6.3.1 Batch Generation of VLPs This section describes the process of batch generating VLPs in PROSPER and transferring the information to GAP. As with the batch transfer of IPRs as described before, it is of course necessary to have appropriately prepared PROSPER files for each well and also to have these PROSPER files referenced on the well summary screens. The process of referencing the PROSPER files is described in the introduction of the "VLP/IPR Generation" section of this manual. The following description assumes that PROSPER models have been built for each well and referenced from within GAP. To generate the VLPs click "Generate

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And the screen shown below will be presented:

If no wells have previously been selected then this screen will be displayed:

This can be used in the same way as discussed for well selection during "Batch Transfer of IPRs". To generate VLP tables for GAP, check the For GAP model box. PROSPER will be used to 1990-2011 Petroleum Experts Limited

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calculate and save a *.VLP file (GAP Binary VLP lift curves). If the “For Simulator” option is selected then it is necessary to select a target simulator lift curve format from the list selected and an Injection Rate Type (GLR/Gas Injection Rate). The PVT Method drop down box enable to select which PVT dataset is to be used to generate the VLPs, either following the PROSPER model, using a blck oil PVT model or a full compositional PVT model if available.

The “For GAP model” option must be used when modeling pipeline Pressure and Temperature in GAP. No other VLP format allows for transferring the temperature values from the well models to the surface network. For Gas Lift wells, it is possible to select the sensitivity variable type as: Either "GLR injected" Or "Gas Lift injection rate" It is recommended to use the "GLR injected" sensitivity variable as the range of variable will be independent of the wells' productivity. The range recommended for the GLR injected is (in scf/STB): 0, 100, 200, 400, 800, 1600, 3200, 6400, 12800, 25000.

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Check the “For GAP model” option and Click the Data button. GAP will start PROSPER and recall the .ANL file for each selected well. The .ANL files contain the values of sensitivity variables to be used in the VLP calculations. Once all the well files have been read the screen shown below is presented. To check and edit the values, click the Edit button for the corresponding factor. The following screen represents the factors to be entered for a naturally flowing well.

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The populate buttons shown above can be used to fill in the table with numbers:

Enter rates (up to 20) and values of manifold pressure, GOR and water cut into the VLP table to be used for generating the VLP curves. Click the |OK button to exit the data screen. The values used for generating the VLP curves are dependent upon the conditions of the field. The objective is to generate the VLP curves with a range of values that encompass the conditions that will be experienced in the well/field in future. The reason for using a high range of values is so that GAP will always interpolate between the GAP User Guide

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values entered. If the range of data points entered is sparse, then GAP will have to extrapolate on the values which may give incorrect results. A possible range of values that can be used for the generation of VLP's can be found be clicking here 408 . Once the rates, pressures etc. have been entered correctly for each selected well the OK button can be pressed to return to the selection screen. The VLP generate variables are saved in the well .ANL files. GAP is now set up to batch calculate the well VLP curves. Before Generating the VLP curves, make sure that the correlation used in the PROSPER corresponds to the correlation that is matched to the well test data (if any). When the Generate button on the VLP Generation screen is pressed GAP will automatically direct PROSPER to calculate VLP curves for each selected well using the rates and sensitivity variable values entered in the GAP VLP data table. PROSPER will automatically save the VLP tables in the appropriate file format. In the version 8 of GAP (IPM 7) the VLP generation process has been made much faster by working with the PROSPER model in background and not opening the PROSPER model in the Windows interface. In past versions the PROSPER model was opened directly. The progress of the VLP generation can be followed by means of a progress bar that shows the time elapsed and the time remaining to complete the calculation.

VLP calculations can take a considerable time if many rates and variables are used. Before starting the run, check the PROSPER files carefully to avoid problems that may halt the automatic process. To maximise efficiency, plan to Generate Well VLPs when the computer is not in use (overnight). Once the generation is successfully completed, a screen notifying the user of the completion of the task will be shown. The process is now complete. It is recommended that the VLPs are inspected at this stage to ensure that the calculated values are consistent. This is done by opening an appropriate well 1990-2011 Petroleum Experts Limited

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data input screen and selecting |Summary |Lift curves |Inspect.

2.6.3.2 Values to use for VLP Generation The values used for generating the VLP curves are dependent upon the conditions of the field. The objective is to generate the VLP curves with a range of values that encompass the conditions that will be experienced in the well/field in future. The reason for using a high range of values is so that GAP will always interpolate between the values entered. If the range of data points entered is sparse, then GAP will have to extrapolate on the values which may give incorrect results. The following values can be used as possible intervals to enter the data for the VLP curves. These values are only provided as guidance. The user has the best understanding of the production system, and therefore is the best person to decide on the range of values to be used. It is the responsibility of the user to cross check if the field conditions observed for a particular well lie within the range of data entered for the VLP curves. For Naturally Lifted Oil Wells. From Liquid Rate

To

From low AOF value (say (Absolute 100 stb/d) Open Hole Flow of well)

Number Distribution Comments of Points of Points 20

Geometric Spacing

Top Node From Pressure separator pressure value (for example, 100 psig)

Reservoir Pressure

10

Linear Spacing

Water Cut 0 %

90% or 95 10 % or 99 %

Linear Spacing

GOR

25000 scf/ stb

Geometric Spacing

A value less than Solution GOR

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Pressure just falls below the bubble point.

For Gas Wells From

To

Number Distribution Comments of Points of Points

From low value (say 0.1 MMscf/ d)

AOF (Absolute Open Hole Flow of well)

20

Geometric Spacing

Top Node From Pressure separator pressure value (for example, 100 psig)

Reservoir Pressure

10

Linear Spacing

The Top Node Pressure corresponds to the Well Head Pressure.

WGR

0

Refer to Comments on the Right

10

Linear Spacing

The value for Maximum WGR is dependent upon the fluid properties. Generally a value of 100 stb/MMscf is reasonable.

CGR

0

Refer to Comments on the Right

10

Geometric Spacing

The value for Maximum CGR is dependent upon the fluid properties. Use a value slightly greater than the reservoir CGR

Gas Rate

For Retrograde Condensate Wells

Gas Rate

From

To

Number Distribution Comments of Points of Points

From low value (say 0.1 MMscf/ d)

AOF 20 (Absolute Open Hole Flow of well)

Geometric Spacing

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Top Node From Pressure separator pressure value (for example, 100 psig)

Reservoir Pressure

10

Linear Spacing

The Top Node Pressure corresponds to the Well Head Pressure.

WGR

0

Refer to 10 Comments on the Right

Linear Spacing

The value for Maximum WGR is dependent upon the fluid properties. Generally a value of 100 stb/MMscf is reasonable.

GOR

0

Refer to 10 Comments on the Right

Geometric Spacing

The value for Maximum CGR is dependent upon the fluid properties. Use a value slightly greater than the reservoir CGR

For Artificially Lifted Wells The VLP Data section for Artificially Lifted Wells requires inputting a fifth variable. The following table shows the variables and values for different types of Artificially Lifted Wells. Variable

Values

Gas Lifted GLR Injected or 0, 100, 200, 400, 800, Wells 1600, 3200, 6400, 12800, 25600 (in scf/ stb) Gas Lift Gas Rate

Comments Using the GLR Injected as a variable will ensure that the VLP curves will always interpolate for the Gas Lift Gas Rate. Enter the range of values that could be injected in the well

ESP wells Frequency of Operation

Depending on the Variable Frequency Drive Option, enter the range of values for the frequency of motor operation. These generally range from 40 to 70 Hz.

PCP Well Motor RPM

The Motor rpm corresponds to the Pump Speed.

Jet Pump Power Fluid Well Rate HSP Well Pump Rotational

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Speed

For GAS Injection Wells From

To

Number Distribution Comments of Points of Points

From low value (say 0.1 MMscf/ d)

AOF (Absolute Open Hole Flow of well)

20

Geometric Spacing

Top Node From low Pressure value (for example, 100 psig)

Reservoir Pressure

10

Linear Spacing

The Top Node Pressure corresponds to the Well Head Pressure.

WGR

0

Refer Comments on Right

10

Linear Spacing

The Maximum Value for WGR is dependent upon the quality of the gas being injected. Generally a value of 50 stb/MMscf is reasonable.

CGR

0

Refer Comments on Right

10

Geometric Spacing

The Maximum Value of CGR is dependent upon the quality of the gas being injected.

Gas Rate

For WATER Injection Wells From

To

Number Distribution Comments of Points of Points

Liquid Rate

From low AOF value (say (Absolute 100 stb/d) Open Hole Flow of well)

20

Geometric Spacing

Manifold Pressure

From low value (for example, 100 psig)

10

Linear Spacing

Reservoir Pressure

The VLP calculation data can be easily copied from one well to another using the copy and paste function. Click in the check box next to the well with the data to 1990-2011 Petroleum Experts Limited

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be copied so that a cross appears. Click on the copy button at the bottom of the dialogue screen. Then click in the check box next to the well that the data is to be copied to and press paste. The range of the variables entered for the first well will be copied to the currently selected well. When copying data from one well to another, it should be ensured that the data cover the operating range of the new well. 2.6.3.3 Generating Well VLP on a well-by-well basis The generation of a VLPs can also be carried out for an individual well by following the procedure below. This method may be preferable if a model is small or if additional wells are being added to an existing GAP model. The procedure is as follows for generating the VLP file in PROSPER is as follows: 1. Load PROSPER from Windows or from the well data entry screen and open (or create) an appropriate PROSPER well file. 2. The VLP curves for the file for a naturally flowing well can be generated by selecting | Calculation |VLP Tubing Curves|(3 Variables) from the menu bar. For a gas lifted well select |Calculation |VLP Tubing Curves|(4 Variables) from the menu bar.

3. Enter the top node pressure and water cut values into the input table and a range of liquid rates that encompass the full range of operating conditions into the table at the bottom screen. Now press the |Continue button at the top of the screen. This will display the sensitivities screen shown below:

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For a naturally flowing well the first node pressure, GOR and water cut must be varied. For a gas lifted well the Gas lift injection rate must also be varied. An error message will be displayed and the created file will not be useable in GAP if variables other than the above are varied. 4. To start the generation of the VLP’s click |Continue which will display the “VLP (tubing curves) calculation screen” followed by |Calculate to begin the calculations. The “VLP (tubing curves) calculation screen is shown below:

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5. Click the |Export Lift Curve button on the Calculation screen. A list of Export formats appears – GAP is able to read lift curves in Eclipse (.ECL), MBAL (.MBV), and GAP (. TPD) formats. Select one of these from the list, and save the file to a suitable location. To import the file into GAP open the appropriate well VLP screen in GAP 6. From the well VLP input screen, click on the Import button. Locate the file that has just been exported from PROSPER using the browser, and press OK. GAP will generate a . VLP file, and the name will be displayed in the VLP file field of the dialog. 2.6.3.4 Batch Generation of VLPs with Mass flow rates The classic definition of VLP curve is that the VLP provides with a relationship between the rate flowing and the bottomhole pressure considering the pressure losses from wellhead (or, more in general, the manifold downstream to the well) to the bottomhole (top perforations), as a function of the operating conditions (manifold pressure, WC and GOR). In this definition the flow rates are defined as volumetric rates at standard conditions (STD). As the volumes at standard conditions are dependent on the way the fluid is processed down to STD, they will depend on the specific path followed to STD. In other words, the same mass of fluid flowing will have a different flow rate depending on the path to STD used to express the rates. Defining the rates in terms of mass has got the great benefit of making the rates (hence the VLPs) process independent. This is because volumetric rates at standard depend on the process used to analyse the fluid, whilst mass is invariant, therefore does not depend on the process used. This option is particularly useful when coupling GAP User Guide

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models having different reference paths to standard: using the mass one does not have to re-generate IPRs and VLPs if the process changes. When one of the compositional PVT models (see above 128 ) is selected, it is possible to generate the lift curves with mass flow rates. To achieve that: The PROSPER well model should be set to Equation of State:

In GAP, well Summary screen (accessible by double-clicking on the well), the option to use the Mass rates should be enabled:

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Generate the VLPs directly in PROSPER as showed in the section above 412 . In PROSPER the Rate Type selected in the VLP calculation section should be selected as Hydrocarbon Mass Flow Rate :

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Note that the variable GOR to use should be replaced by Molecular Weight, whilst all the other variables should be the same as the volumetric rate VLPs. For example, the screenshot below shows the variables to enter for a gas retrograde condensate well:

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2.6.3.5 Batch Generation of Pipe VLPs The batch generation of Pipe VLPs has been added to GAP to allow lift curves to be generated for pipes that have been defined using the new PROSPER in line features or for which the “use lift curve” option has been selected from within the pipe summary screen. The procedure for generating pipe VLPs is similar to well VLPs. Select |Generate |Generate Pipe VLPs from the GAP menu bar. If no wells have been selected, then the screen shown below will be displayed.

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Clicking on all will select the pipes in the system that has the ‘Use lift curves’ option selected.

Clicking on |Data will display the ‘generate data’ screen shown below:

This should be used as described in the user Guide for well VLP generation. Ensure that the values specified in the table encompass the full spectrum of operating conditions that will be encountered.

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It is advised to include negative rates, as the fluid can potentially flow in both directions. Repeat this process for each of the pipes that have been selected. Clicking on the |Ok button will return control to the ‘Generate’ dialogue screen above. From this screen, press the generate button to begin the batch generation of the pipe VLPs. Once this is successfully completed the software will prompt a message notifying the user of the completion of the task. It is recommended that the VLPs are inspected at this stage to ensure that the calculated values are consistent. This is done by opening an appropriate pipe data input screen and selecting |Summary |Lift curves |Inspect.

2.6.4 Batch Generation of Well Performance Curves This section describes the process of batch generating Performance Curves for the GAP well models, using the well VLPs and IPR previously generated. We will note that the Performance Curves (PCs) are going to be generated for unique values of Reservoir Pressure, WC (or WGR for gas wells) and GOR (or CGR for dry gas wells). During a Prediction, the PCs are re-generated before each timestep using the WC, GOR and Reservoir Pressure coming from the tank models associated to the wells. In order to batch generate the PCs, the wells model need to have previously been changed to "Performance Curves" or "PC interpolation" (the "Performance curves" model fits a polynomial curve to the PC points, whereas the "PC interpolation" model linearly interpolates between the PC points). One can decide to select and modify all the wells models in one go by: 1. Selecting all the wells:

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2. Changing the well models to "PC Interpolation":

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can be followed, just like in the case of well VLP generation 402 :

If no wells have previously been selected then this screen will be displayed:

This can be used in the same way as discussed for well selection during "Batch Transfer of IPRs". When the wells are selected from the list below, click "Continue":

On the table below, the well are listed accordingly to their types (Naturally flowing, Gas lifted, ESP...):

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As mentioned before, the WC, GPR and Reservoir Pressures are unique. They are by default coming from the well IPR sections. However, one can decide to use those information from the "Wells Model Validation" screen, using the "Transfer" button. The 10 different Manifold Pressure can be entered by hand, or selected automatically, using the "Automatic WHP" feature, as shown below:

We use the "Generate" button to generate the Performance Curves. Note on Gas Lift wells: For Gas Lift wells, the Performance Curves are generated for two variables; the Manifold Pressure (as the other wells) and the Gas Lift Injection Rate.

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Like for the other wells, the range of Manifold Pressure has to be entered. The range of GLR injected (or Gas Lift Injection Rate) is then automatically selected by GAP, in order to always get the maximum of the PC curves. Note on the Performance Curves: Since the PC is a curve fitted on a number of points, this may cause interpolation approximations. Using the VLP/IPR intersection method instead, linear interpolation is applied between the VLPs, thus limiting the amount of error that can be introduced to a minimum. NEW!!! In the current version of GAP the PC curves are characterised by 20 points, which makes them very accurate and avoid the issue highlighted above. The VLP/IPR intersection method should be the preferred one. Using PC's might however speed up the calculation for big systems. It will eventually be noted that generating Performance Curves ("with VLP/IPR") can help highlight issues in the quality of the VLPs.

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2.7 Model Validation In any GAP model it is important that the well models used can reproduce measured well data reasonably well. This section introduces the user to the Model Validation menu option in GAP, which allows efficient quality checking of the well models in GAP against measured data, with the ability to trouble shoot individual wells. This also allows verifying if they are able to reproduce current test data and update the well models (e.g. IPR) if required.

This chapter describes the validation of well models in GAP using the |Model Validation menu options. The well performance model considered can be: Performance Curves VLP / IPR intersection

2.7.1 Well Model Validation The following assumes that the PROSPER well model is accurately matched to measured production data. The following steps outline how to ensure that the accuracy of the PROSPER model has been preserved within GAP. The accuracy of the well models must be checked before attempting an optimisation. The following sections go through the quality check procedure for the well models.

2.7.2 Checking Wells Calibration Model Validation is based on reservoir pressure, water cut GOR (oil producer wells) and measured manifold pressures from a test. GAP uses either the performance curves entered or the VLP and IPR curves that are in the well-input screens and calculates well production rates for the flowing conditions specified. The calculated well rates are displayed against the measured rates and an overall liquid error is indicated. Changes can then be made to the model in order to respect the measured data.

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2.7.2.1 Running Model Validation / Quality Check To carry out a Model Validation calculation, enter the following screen by selecting Model Validation | Well Models Validation from the main screen of GAP.

On entering the dialogue, select the well type to work with and whether the oil or liquid rates should be used when entering rates. This may depend on the measured data available The values of Reservoir Pressure, Water Cut and GOR present in the well’s IPR screen can be transferred to this screen. In the case of the Gas producer Wells, the values of WGR and CGR will be transferred. This is done by using the Transfer button located at the bottom of the screen:

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Select the Transfer from IPR / VLP option. The option Transfer to IPR / VLP option enables to transfer the data from the validation screen to the IPR / VLP section of the wells considered.

NEW!!! The Transfer menu allows to transfer to the Model Validation the well test data from the PROSPER well model by selecting Transfer/Transfer latest Well Tests from associated PROSPER files, as shown below:

The wells to select can be chosen from the well list displayed.

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If required, the transferred data (Reservoir Pressure, GOR, WC) can be changed accordingly to the actual measured data. For the wells described with performance curves, the reservoir pressure column will be disabled. The Import button can be used to import a dataset from a text file. The Paste button can be used to transfer data from Excel using the Copy + Paste route. Once part of the dataset has been transferred using the Transfer button, it will be possible to enter the Manifold Pressure and Liquid Rate (or Gas Rate) according to the measured data. For artificially lifted wells, the artificial lift quantity will only be updated automatically via the transfer option if the existing artificial lift quantity data has first been deleted from the model validation table.

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Click the Calculate button and GAP will use the VLP tables and evaluate the IPR for the current producing conditions as entered in the individual well input screens, and use them to calculate production rates for each well:

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Rates are marked with a contrasting colour if the lift curves were extrapolated to find a solution. In the case of a multi-layer IPR model, GAP will use the layer pressures used in the well IPR entry screen and will disable the reservoir pressure column. Once the calculation has been done, the user can compare the measured rates versus the calculated rates of the model and in case there are significant differences, identify the well and check visually the error. The difference between the calculated rates and the measured ones.

2.7.2.2 Checking the Quality of Individual Wells Graphically If a well has large deviation between measured and calculated rates, select the Edit button to access the well input screen for troubleshooting purposes.

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VLP and IPR intersections can be viewed by pressing the Plot button.

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VLP and IPR intersections can be viewed by pressing the Calculate button in the well summary screen. On this screen, click on Plot and a plot of the intersection as generated by GAP can be seen.

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Once the reason for the discrepancy between measured and calculated well performance is identified, any required adjustment can be done (e.g. PI adjustment, VLP re-generation with a more appropriate range of values). As a final step, the values of Reservoir Pressure, Water Cut and GOR can be transferred back to the well’s IPR screen by using the Transfer button as illustrated previously, using the option “To VLP/IPR screen”. This step is required if GAP is to update the existing values in the wells with the current measured values. While troubleshooting check that the IPR PVT and, reservoir pressure etc are identical to that of test. Also check that the set of VLP data used in GAP has the relevant range, i.e. not extrapolating. Note that, in Material Balance Prediction mode, well inflow performances will be calculated using a connected Tank’s PVT calculator. If no tank is connected, GAP will use its own PVT calculator. This could yield slightly different results: when performing a Production Validation calculation prior to performing a prediction, one should connect all the Tanks to the required Wells before performing this operation. GAP will display a ‘No Solution’ message if no intersection could be found.

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2.8 Network Solver and Optimiser This chapter describes how GAP solves the surface network system for pressures and rate at various nodes / points within the system once the system is defined. A defined system consists of the following: All wells with valid inflow / VLP data or Performance Curves All pipelines and other surface equipment defined and calibrated.

2.8.1 The Solver The solver in GAP essentially generates a set of mass balance equations and pressure balance equation at each joint in the system as indicated in the Core GAP technique 15 . In this way a set of equations for the whole network is generated. Then these equations are solved simultaneously, given the boundary conditions, which are fixed separator pressures. The solver is used to find the pressure and flow distribution in the surface network given the fixed separator pressures.

2.8.2 The Optimiser GAP contains a powerful non-linear optimisation algorithm (NLP) for naturally flowing, gas lifted and injection wells. GAP will optimise oil production by simultaneously adjusting well chokes, gas lift gas injection rates, ESP frequencies, pump/compressor speed etc as applicable. If, after reducing the lift gas injection rate to zero for a gas lifted well, the well production must be further reduced to meet a constraint for example, GAP can automatically choke wells back. Please refer to the section on the Optimiser 16 for further details.

2.8.3 Constraints and Equipment Control Screen 2.8.3.1 Constraints Constraints can be used to choke wells back to meet production targets or processing limitations while optimising oil production. By careful use of maximum and minimum well constraints, the user can give priority to, for example, high water cut wells while allowing other wells to be choked back to meet overall constraints. The Optimiser in GAP is designed to optimise the returns of the objective functions, which could be the oil produced, revenue earned or gas produced depending on the options selected as defined in next section. The Optimisation done is subject to the constraints entered at various levels in the network. The results of the optimisation will be the following:

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Naturally Flowing Wells (Wellhead dP) Inflow Elements (down-hole dP) Gas Lifted Wells (Gas Allocated to the Well / dP at well head) Diluent Injection Wells (Diluent Injection Rate / dP at well head) ESP Wells (Frequency of operation / dP at well head) PCP Wells (Speed of operation / dP at well head) HSP / Jet Pump Wells (Power Fluid Injection Rate / dP at well head) Inline Controllable Chokes (dP) Pumps with Control (Speed of rotation) Compressors with Control (Speed of Rotation) Optimised Inline Injection (Gas injection Rate)

When performing optimised runs, the wells in the system should be set controllable (Chokes on the wells that can be controlled by the Optimiser). 2.8.3.2 Equipment Control Screen The equipment control screen enables to monitor the status of the different elements of the system relatively to production validation and optimisation. The equipment control screen can be accessed using the following icon on the shortcut menu bar.

The equipment control screen appears as follow.

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The equipment control screen will display all the system equipment susceptible to be controlled by the optimiser, along with their control variable values. The top part of the screen enables to filter the equipment list either by equipment type and sub type, equipment control type, Optimised only or Non optimised only elements. Once a specific layout has been defined, the Save Layout button enables to save it in memory to be able to use the same layout later on. The bottom part of the screen displays the list of system elements as follow: Equipment Label Control Type Control Mode Measured

Actual

Optimised

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Enables the identification of the element considered Enables to identify which specific parameter of a system element can be controlled by the optimiser Enables to identify whether a specific parameter of a system element is controlled by the optimiser or is set to a fixed value In relation with the model validation facilities (i.e. see Chap 7), displays the current measured value of the parameter considered Displays the current value of a parameter in the system. For instance, if a gas lift gas injection rate for a well has to be fixed, the value of gas lift gas injection will be specified in this section and the control mode set to Fixed value using the Edit button Displays the value of the parameter considered after optimisation February, 2011

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If the control parameter is bounded by a minimum value, displays this minimum If the control parameter is bounded by a maximum value, displays this maximum Refers to the unit used to define the control parameter Enables to go to the Control section of the element considered The Transfer button at the bottom of the screen enables to transfer one set of value from one column of the equipment control screen to another (i.e. transfer optimised parameter values to the actual column for instance). The Transfer button triggers the following transfer screen.

2.8.3.3 Optimisation Objective Function This section defines the objective function used by GAP to optimise the system To define the method of optimisation, click on Options Method and select the optimisation method from the drop-down box as in the following dialogue box:

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Make the selection of optimisation method from the choices provided in the box above: Production

Revenue

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This option optimises the production rate of the primary fluid (in an oil system this is the oil for example). GAP will calculate the maximum rate that can be achieved while honouring production constraints This option optimises on the revenue generated by sales of oil and gas produced after taking into account the cost of processing water and injecting gas. If this option is selected, then prices need to be defined for each fluid in the system (see below). The currency can be defined by selecting "Currency Setup". The following additional data is required to be entered in |Options |Tax Regimes: Revenue from oil sales Revenue from gas sales Cost of water processing Cost of injection gas Cost of power Cost of steam

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Up to 32 different Tax Regimes can be set. The Tax Regime to be used by the system during optimisation can be selected in any well summary screen. The default Tax Regime is selected in |Options |Default Settings. Oil rate only / Those methods are used when the objective is to maximize only the Oil rate, the Gas Rate or the Water rate Water rate only Gas + Oil This method allows to maximise at the same time oil and gas production rate rate only rates and honour constraints Gross This option maximises the gross heating value produced by the field. This Heating Value option is mainly used in the case of gas fields where one would like to maximise the gas heating value of the delivered gas. If the GAP model contains various streams of gas that will contain different compositions and hence gravities, the optimizer will control the system in order to provide at the delivery point a blend of gas that can have the highest possible heating value. In black oil mode, the program will use a correlation to associate the heating value to the gravity of the gas (Figure 4.82 in the Handbook of Natural Gas Engineering published by McGraw-Hill).

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2.8.4 Solving the Network There are three Network Solving modes to know, No optimisation Optimise and honour constraints Optimise, no constraints These options will be discussed later in this section. To perform the Network Solving on the main GAP menu chose Solve Network and then "Run Network Solver...".

If there is any gas lifted wells, the gaslift gas available will be required.

Up to ten different cases can be set. The values set in this screen will be only used when the network is solved with Optimisation. Otherwise, the gas injection rates for each well will be taken from the |Actual |Actual screen. Click on Next to specify the separator pressures

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If there is no gas lifted wells, up to ten different Separator Pressures (cases) can be specified. Once the separator pressure is defined, click on Next. This leads to the Solver screen as shown:

On this screen, the Optimisation mode can be selected before performing the calculation. Click "Calculate" to run the solve network.

2.8.5 Solver Modes This section describes the different modes that can be selected when solving the network:

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2.8.5.1 No Optimisation This option invokes the solver only. GAP will calculate the pressures and rates at various points in the network. The solution is according to the following criteria: No constraints specified are honoured For artificially lifted wells, the solver takes the corresponding artificial lift parameter value for each well from the Equipment Control screen under the section Actual For all Equipments with dP Control (Wells and online Chokes) specified as calculated, the dP is taken as specified in the Equipment Control screen under the section Actual For all Equipments with dP Control (Wells and online Chokes) specified as a fixed value, the specified value is used

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2.8.5.2 Optimise with all constraints This option invokes the solver and the optimiser as well. GAP will optimise the Production / Revenue honouring the specified constraints. The solution is according to the following criteria: All specified binding constraints are honoured (provided they are feasible). For artificially lifted systems, the optimiser allocates the artificial lift parameter value in such a fashion that overall production is optimised. For all Equipments with dP Control (Wells and inline Chokes) specified as Calculated, the dP is calculated so as to yield an optimum solution. For all Equipments with dP Control (Wells and inline Chokes) specified as a fixed number, the specified number is used. If this mode is selected, an option to also calculate the potential becomes available. If this option is checked, GAP will also report the optimum calculated values that could be obtained if the constraints were ignored. Note: The constraints that have the "Potential" option turned to "Yes" will still be considered and honored during the potential calculation.

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2.8.5.3 Optimise with potential constraints only GAP will optimise the Production / Revenue only honouring the "potential" constraints. Those are the constraints for which the "potential" option is turned to "yes" in the constraint table. The constraints which have the "potential" option turned to "no" are ignored during this calculation.

2.8.6 The Solver / Optimiser Settings The Solver and the optimiser both use numerical schemes for solution. For these schemes, the derivatives (rates of change) need to be calculated numerically. Also, we define various tolerance criteria to check for convergence. All these are defined under the Settings. The settings button is seen in the Solver / Optimiser screen as shown below:

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Selecting the “Settings” button will prompt the following screen with the default settings:

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GAP offers various settings configurations. For most cases, the default configuration should be OK. However, for complex systems, the experienced user may select a different configuration, better suited to their needs. The following configurations are available: Default Fastest but may be less accurate in small systems Large System (to speed up) Quick and Rough Tight tolerance (slower) To change a Base Configuration, click on the drop down list box, selected the base configuration that you wish to change to. Then, click on the ‘Apply’ button, followed by the ‘Reset’ button. Beyond this, the experienced user may customize the various settings. GAP User Guide

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Below are some guidelines to the settings available: Solver - Max iterations

Solver - Jacobian Term Multiplier Solver - pressure perturbance Solver - Total Rate Perturbance

Solver - pressure balance normalizer

Solver - well initial rate fraction

Solver - tolerance F

Solver - tolerance min Solver - tolerance X Solver - Maximum Step Size

This is the maximum number of iterations the solver is allowed to perform in order to converge. If convergence has not been achieved within this number of iterations, then the solver will simply stop. However, in most systems the solver will require much less iterations than 50 (the default number) so if convergence has not been achieved, this may indicate a problem in the model setup which prevents the solver from finding a solution This parameter exaggerates the slopes (derivatives) hence a faster solution can be achieved if this value is increased. However, there is the possibility that by increasing this value, the solver may overshoot and cause problems with the convergence The GAP network Solver works with derivatives which are created with a certain change in pressure. This delta in pressure defines the magnitude of perturbation (in psi) This is the total rate used to calculate the derivatives (as with the pressure perturbance described above). A value of 1 (Mstb/ day or MMscf/day depending on the system being oil or gas) is the default one and should be fine for most cases. If the model contains chokes and long pipelines with small ID for instance, it is recommended to reduce the total rate disturbance to 0.1 or 0.01 as appropriate Used to normalize the derivatives of dp/dDp and dq/dDq. It defines the relative weighting of the pressure balance error relative to the rate error. The smaller the value the more accurate the balance will be, but then the more difficult it is to converge It is the fraction of the initial rates (generated from wells using separator pressures as back pressure) that is used to get the first guess for the solver. The default is 1.0. In some long pipeline systems or small pipeline systems, or systems with chokes, where the initial rates are difficult to pass, setting a smaller number may increase speed of convergence. In such a case, one might reduce the initial rate fraction, to 0.1 for instance This is the root mean square of the errors in the material balance and pressure differences at any node. The higher this number, the higher the error in mass/pressure at each node, but the faster the solution. The default is 0.1 Do not change Do not change The solver line search will limit the change from one iteration to the other by this value 1990-2011 Petroleum Experts Limited

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Solver - Mass to Volume Scaling

In IPM 4.0 and earlier, GAP was performing the calculations based on volumes. IPM 5.0 can be fully compositional so all the calculations are done based on mass. This value can be used to scale up or down the volume given by a particular amount of mass in the system Solver - Limit In certain cases derivatives can be very difficult to calculate because of extremely rapid changes or extremely low changes movement of in the system. This parameter limits the movement of the derivative derivatives and attempts to get something meaningful from the system. Minimum number is 0 and maximum 1 Solver - display This setting allows the user to display the pressure and mass results in the network on the solver display screen during solver (0:none, 1:pipe, iteration. 2: eqns, 3: pipe+eqns) 0: No intermediate results are displayed 1: The intermediate results for the pipes are displayed 2: The intermediate residuals of equations at the nodes displayed. 3: The intermediate residuals of equations at the nodes and the pipes are displayed. The default is 0 and does speed up the calculation time Solver - Inflow Crossflow This setting can be set to 0 or 1. If it set to 1, then cross-flow in an inflow element is not allowed (cross-flow is prevented). If Control (0:Off, 1:On) instead it is set to zero (default), then cross-flow is allowed to occur Solver - report When running any calculation in optimisation mode the program will highlight eventual limiting or violated constraints. violated /limiting In the case the calculation is run in no optimisation mode the constraints without program will run the system without changing controls, therefore optimisation in no optimisation mode the constraints will not be accounted (0:Off, 1:On) for. This setting allows to activate a report showing if a constraint is violated or limiting for the system when the calculation is run without optimisation Optimiser - max This is the maximum number of iterations the optimizer is allowed to perform in order to converge. The default is 100 iterations Optimiser - well This is the fraction of the normalized system potential used for the first guess. If there are small chokes and long pipelines in initial rate fraction the system, a smaller value (0.1) could be used, in order to ensure that the calculations do not start with critical conditions at these elements. Another case where the well initial rate fraction may require reduction to 0.1, is when there are constraints which are very small compared to the potential of the wells. So the optimiser will reach the constraints by increasing the rate of the wells, instead of the conventional rate reduction than might pose problems in such a case (optimiser not 'seeing' the constraints). GAP User Guide

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User Guide

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The default is 1 Optimiser - gas For gas lifted systems, this defines the gas lift gas injection rate used to perturb the system. The default is 0.1 and should work injection perturbance for most cases Optimiser - frequency For ESP lifted system, this defines the magnitude of frequency used by the optimizer in perturbing the system. The default is perturbance 0.1 and should work for most cases Optimiser - rpm If there are surface pumps and/or compressors in a network and pumps lifted system, this defines the magnitude of perturbance revolutions per minute used by the optimizer in perturbing the system. The default is 100 and should work for most cases Optimiser - max In simple terms, this parameter will determine whether a constraint is seen and whether it should be included in the step size matrix. The higher this number is, the further the algorithm sees to include violated constraints as part of the matrix. On the other hand, a high value will lead to greater changes and a more complicated problem. An inequality g is binding if g/max {1, || grad g||}