• Author / Uploaded
• Filipe Af

Citation preview

Reservoir Geomechanics In situ stress and rock mechanics applied to reservoir processes     Mark D. Zoback  Professor of Geophysics   

Week 1 – Lecture 2 The Tectonic Stress Field

Stanford|ONLINE gp202.class.stanford.edu

Outline Section 1 •  Basic Definitions •  Anderson’s Stress Classification Scheme •  Stress Orientations Near Salt Domes Section 2 •  Stress Magnitudes at Depth •  HW -1 Calculating Sv Section 3 •  Measuring In-Situ Stress •  Regional Stress Patterns •  Local Stress Perturbations Stanford|ONLINE gp202.class.stanford.edu

2

Stanford|ONLINE gp202.class.stanford.edu

Figure 1.1 – pg.6

3

Components of a Geomechanical Model Principal Stresses at Depth Sv – Overburden SHmax – Maximum horizontal principal stress Shmin – Minimum horizontal principal stress

Sv

Additional Components of a Geomechanical Model

UCS Pp

Shmin Stanford|ONLINE gp202.class.stanford.edu

SHmax

Pp – Pore Pressure UCS – Rock Strength (from logs) Fractures and Faults (from Image Logs, Seismic, etc.) 4

Zoback and Zoback (1980, 1989) Stanford|ONLINE gp202.class.stanford.edu

5

Generalized World Stress Map 180

270

0

90

180

70

70

35

35

0

0

SHmax in compressional domain

-35

-35

SHmax and Shmin in strike-slip domain Shmin in extensional domain

180

270

0

90

180 9-2

Stanford|ONLINE gp202.class.stanford.edu

6

Complex Stress State Surrounding Salt Domes

Stanford|ONLINE gp202.class.stanford.edu

7

Salt Bodies in the Gulf of Mexico

Figure 1.10a – pg.25 Stanford|ONLINE gp202.class.stanford.edu

8

Schematic Stress Contours

Figure 1.10b – pg.25 Stanford|ONLINE gp202.class.stanford.edu

9

Anderson Classification of Relative Stress Magnitudes Sv

Normal

SHmax

Shmin

b

Shmin SHmax a.

Strike-Slip

Sv > SHmax > Shmin Sv

Shmin

SHmax

Shmin SHmax > Sv > Shmin Sv Reverse

b.

Shmin

shmin Tectonic regimes are sv Normal in terms defined of the SHmax relationship between the vertical stress (Sv) X and two mutually perpendicular Strike-slip horizontal stresses SHmax (SHmax and Shmin) sHmax

SHmax Shmin c.

SHmax > Shmin > Sv

Stanford|ONLINE gp202.class.stanford.edu

Reverse Map View

sv Cross-section

10

Relative Stress Magnitudes and Faulting Regimes

Regime/Stress

S1

S2

S3

Normal

Sv

SHmax

Shmin

Strike-Slip

SHmax

Sv

Shmin

Reverse

SHmax

Shmin

Sv

Table 1.1 – pg.8

Stanford|ONLINE gp202.class.stanford.edu

11

Anderson 1 – Faulting Styles Sv

Normal

SHmax

Shmin

b

Shmin

shmin

SHmax a.

Strike-Slip

Sv > SHmax > Shmin Sv

Normal SHmax

Shmin

X

SHmax

Shmin SHmax > Sv > Shmin Sv Reverse

sv

Strike-slip

b.

SHmax

Shmin

sHmax

SHmax Shmin c.

SHmax > Shmin > Sv

Reverse Map View

Stanford|ONLINE gp202.class.stanford.edu

sv Cross-section

Stereonet 12

Anderson 1 – Faulting Styles

Normal

Sv

SHmax

Shmin

b

Shmin

s Geologic Structures Reflect sEither Normal Sv > SHmax > Shmin a. Past Sor Current SStressS Fields (or Both) Strike-Slip but X S In This Class We are Almost Always S Strike-slip b. Going SHmax v > Shmin to> Sbe Interested in the Current Stress State

SHmax

hmin

v

v

hmin

Hmax

Shmin

SHmax

Hmax

hmin

Reverse

Sv

sHmax

SHmax Shmin c.

SHmax > Shmin > Sv

Reverse Map View

Stanford|ONLINE gp202.class.stanford.edu

sv Cross-section

Stereonet 13

Figures 5.1 a-d – pg.141 Stanford|ONLINE gp202.class.stanford.edu

14

Limiting cases Radial Extension Sv >> Shmax = Shmin

Anderson’s Classification Normal faulting (NF) Sv > Shmax > Shmin

Intermediate cases Normal/Strike-Slip faulting Sv = Shmax > Shmin

Strike-slip faulting (SS) Shmax > Sv > Shmax

Strike-Slip/Reverse faulting Shmax > Sv = Shmin

Reverse faulting (RF) Shmax > Shmin > Sv Radial Compression Shmax =Shmin >> Sv

Stanford|ONLINE gp202.class.stanford.edu

15

Variations of Regional Stress Magnitudes

Hurd and Zoback (in press)

Stanford|ONLINE gp202.class.stanford.edu

16

Stress Orientations in North America

Stanford|ONLINE gp202.class.stanford.edu

17

Anderson 2 – Classification of Relative Stress 180

270

0

90

180

70

70

35

35

0

0

SHmax in compressional domain

-35

-35

SHmax and Shmin in strike-slip domain Shmin in extensional domain

180

270

0

90

180 9-2

Stanford|ONLINE gp202.class.stanford.edu

18

Outline Section 1 •  Basic Definitions •  Anderson’s Stress Classification Scheme •  Stress Orientations Near Salt Domes Section 2 •  Stress Magnitudes at Depth •  HW -1 Calculating Sv Section 3 •  Measuring In-Situ Stress •  Regional Stress Patterns •  Local Stress Perturbations Stanford|ONLINE gp202.class.stanford.edu

19

Anderson 3 – Critically Stressed Faults As much of the crust is in a state of failure equilibrium, stress magnitudes can be estimated (Chapter 4)

Earthquakes Triggered by Reservoir Impoundment Stanford|ONLINE gp202.class.stanford.edu

20

Limiting cases Radial Extension Sv >> Shmax = Shmin

Anderson’s Classification Normal faulting (NF) Sv > Shmax > Shmin

Intermediate cases Normal/Strike-Slip faulting Sv = Shmax > Shmin

Strike-slip faulting (SS) Shmax > Sv > Shmax

Strike-Slip/Reverse faulting Shmax > Sv = Shmin

Reverse faulting (RF) Shmax > Shmin > Sv Radial Compression Shmax =Shmin >> Sv

Stanford|ONLINE gp202.class.stanford.edu

21

Range of Stress Magnitudes at Depth Hydrostatic Pp

Figure 1.4 a,b,c – pg.13

Stanford|ONLINE gp202.class.stanford.edu

22

Range of Stress Magnitudes at Depth Overpressure at Depth

Figure 1.4 d,e,f – pg.13

Stanford|ONLINE gp202.class.stanford.edu

23

Calculating the Vertical Stress, Sv

SV(z) =

z -

ρ(z)gdz ~ ρgz

∫

0

Considering water depth in offshore areas

Sv(z) = ρwgzw +

∫

0

z ρ(z)gdz ~ ρwgzw + ρg(z-zw)







Equation (1.6) – pg. 9

Stanford|ONLINE gp202.class.stanford.edu

24

Visund Field, Northern North Sea

Stanford|ONLINE gp202.class.stanford.edu

25

Anderson Classification of Relative Stress Magnitudes Sv

Normal

b

Shmin SHmax a.

Strike-Slip

Sv > SHmax > Shmin Sv

Shmin

SHmax

Shmin

SHmax

Shmin

SHmax > Sv > Shmin Sv Reverse

b.

Shmin

SHmax

Hydraulic Fractures shmin Always Propagate sv Normal Perpendicular to the SHmax Least Principal Stress, S3 X In 1948, HF Strike-slip Orientations Were SHmax Hotly Debated, Were They Horizontal, s Vertical, Radial? Hmax

Shmin c.

SHmax > Shmin > Sv

Stanford|ONLINE gp202.class.stanford.edu

Reverse Map View

sv Cross-section

26

S

Anderson Classification of Relative Stress Magnitudes Sv

Normal

b

Shmin SHmax a.

Strike-Slip

Sv > SHmax > Shmin Sv

Shmin

SHmax

Shmin

SHmax

Shmin

SHmax > Sv > Shmin Sv Reverse

b.

Shmin

Hydraulic Fractures shmin Always Propagate sv Normal Perpendicular to the SHmax Least Principal Stress, S3 X What Happens when SStrike-slip hmin ~ Sv? SHmax

(SS/RF Stress Field) sHmax

SHmax Shmin c.

SHmax > Shmin > Sv

Stanford|ONLINE gp202.class.stanford.edu

Reverse Map View

sv Cross-section

27

S

Visund Field, Northern North Sea

Stanford|ONLINE gp202.class.stanford.edu

28

Determining Overburden Stress from Density

Stanford|ONLINE gp202.class.stanford.edu

Figure 1.3 – pg.11

29

Outline Section 1 •  Basic Definitions •  Anderson’s Stress Classification Scheme •  Stress Orientations Near Salt Domes Section 2 •  Stress Magnitudes at Depth •  HW -1 Calculating Sv Section 3 •  Measuring In-Situ Stress •  Regional Stress Patterns •  Local Stress Perturbations Stanford|ONLINE gp202.class.stanford.edu

30

Horizontal Principal Stress Measurement Stress Orientation Stress-induced wellbore breakouts (Ch. 6) Stress-induced tensile wall fractures (Ch. 6) Hydraulic fracture orientations (Ch. 6) Earthquake focal plane mechanisms (Ch. 5) Shear velocity anisotropy (Ch. 8) Relative Stress Magnitude Earthquake focal plane mechanisms (Ch. 5) Absolute Stress Magnitude Hydraulic fracturing/Leak-off tests (Ch. 7) Modeling stress-induced wellbore breakouts (Ch. 7, 8) Modeling stress-induced tensile wall fractures (Ch. 7, 8) Modeling breakout rotations due to slip on faults (Ch. 7)

Stanford|ONLINE gp202.class.stanford.edu

Table 1-2 p. 15

31

Visund Field Orientations

Stanford|ONLINE gp202.class.stanford.edu

32

Stress Map of Northern North Sea

Figure 1.8 – pg.23

Stanford|ONLINE gp202.class.stanford.edu

33

Ice Retreat Model

Stanford|ONLINE gp202.class.stanford.edu

34

Modeled Shmin/Sv Compared to Observations

Figure 9.3 – pg. 272 Stanford|ONLINE gp202.class.stanford.edu

35

Visund Field Orientations

Stanford|ONLINE gp202.class.stanford.edu

36

Modeled SHmax Directions Compared to Observations

Stanford|ONLINE gp202.class.stanford.edu

37

Seismotectonics of Northern S. America

Stanford|ONLINE gp202.class.stanford.edu

38

Stress State in Northern S. America

*Light blue arrow indicates relative motion of the Costa Rica-Panama block with respect to the central North Andean block

Stanford|ONLINE gp202.class.stanford.edu

Fig. 1.9 – p. 24

39

Regional Stress in Western California

Fig. 6.8a,b p. 182 Stanford|ONLINE gp202.class.stanford.edu

40

Stress Map of Southern San Joaquin

Figure 1.6 – pg.21

Stanford|ONLINE gp202.class.stanford.edu

41

Southern San Joaquin Valley

Stanford|ONLINE gp202.class.stanford.edu

42

Complex Stress Field in the Elk Hills Field

Stanford|ONLINE gp202.class.stanford.edu

43

Stress Orientation Rotation Near Fault at 3100 meters

Stanford|ONLINE gp202.class.stanford.edu

44

Modeling Fault-Induced Stress Perturbation at the Wellbore Wall

Stanford|ONLINE gp202.class.stanford.edu

45

Multi-Scale Stress Perturbations

Stanford|ONLINE gp202.class.stanford.edu

Figure 11.10 – pg. 359

46

depth (m)

Fractal-like Stress Fluctuations

-90

S azimuth Hmax

Stanford|ONLINE gp202.class.stanford.edu

0

90

-90

0

90

-90

0

47

90