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• Raul Zela

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• Ciencias de la tierra y de la vida
• Ciencias de la Tierra
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Lab 2: Cross sections, the Kink method, and satellite imagery The purpose of this lab is to learn a new method for constructing realistic cross-sections based on surface geologic data (strike and dips, bedding contacts…). We will also learn how to observe bedding geometry from satellite imagery. Using the measurements obtained from the satellite imagery and our newly mastered “kink method,” we will interpret the subsurface geology in a prospective petroleum region in Peru.

Extrapolating Surface Data to Subsurface Using the Kink Method 1

Surface Data

? Subsurface Structural Geometry ?

Types of Surface Data • bed dips • bed contacts • faults • fold axes • topography • ????

2

Project Surface Data to Subsurface using Kink Method

Kink Method • define dip domains or fold limbs • position axial surfaces that bisect fold limbs • project axial surfaces to depth

3

Kink-Method Solution • axial surfaces merge to form new axial surfaces that also bisect fold limbs • (next step ?) apply faultrelated fold theories to define subsurface fault geometry.

Solution

What does the kink-method assume about the bed geometry (in the initial and final state)? Is this a good assumption? Give an example of both an initial bed geometry and a final bed geometry that might not be well represented by this method.

What is the name of the mechanism of how the fold limb deforms? _______________________________

What is another benefit of using the kink method (as in, what reasonable thing does using it ensure)? What is a geologic circumstance in which this would not be applicable?

Exercise 1: Construct a geologic cross section on your computer with Canvas. Use the kink method and evaluate the proposed well location. Open the file “cross_section1.cvx,” located in the “EPS171_2009/Lab2” folder.

Before you construct the cross section: 1. What type of fold is exposed along the section? _______________ 2. Is the well properly located to penetrate the the reservoir at the fold crest (assume a vertical penetration)? ___________________________ Canvas is a handy program for creating illustrations. Here are a few tips to get you started: Create lines using this button : Change the angle of your line on the toolbar at the top of the screen: Measure an angle by clicking

, then choosing

Once you have constructed your cross-section using the kink method, print out a copy and attach it to your lab.

After you have constructed the cross section: 1. Re-evaluate the proposed location. What is the vertical drilling depth to the reservoir?

You can do this exercise if you want more practice using the kink method—but it is not required! There is a Canvas file of this exercise called “Lab2_extra.cvx” in the course folder.

Exercise 2: Petroleum prospecting using satellite data and the kink method Congratulations! You have been hired (for lots of $$$) by a petroleum company to be a part of its exploration team. Even more exciting, you have heard from local sources that there are natural gas seeps in a remote portion of the rain forest in Peru. You talk to your boss about it, and he is interested, so he tells you to assemble a preliminary report to submit to management, arguing your case, which is to drill a test well in the region. Part 1: Locate the major anticlines and synclines using landforms that indicate dipping beds. Your boss gives you the satellite imagery over the area, draped over a DEM for you to use in GoCAD (Lab2/Peru.gprj). Using these data, you will want to identify the synclines and anticlines in the region. You can recognize them by identifying landforms that indicate dipping beds and plunging folds. Tape your map to your desk (just so it stays in place) and tape a piece of mylar over it. Mark the four corners of the map on the mylar. (Alternatively, you can make your map in Canvas – Lab2/Peru_basemap1.cvx – just be sure to save a copy to your own folder). 1) Map landforms that indicate dipping beds and plunging folds using the following symbols:

Outcrops

Drainages

bed contacts

flatiron

flow direction

bedding dip direction

2) Identify changes in the strike and dip that indicate large-scale folds and fold plunge. Map major fold axes with lines and the following symbols on the mylar:

syncline

anticline

3) Good news! Your project manager convinces a geologist at the field office in Cusco to go out to the field region and collect a few strike and dip measurements (Lab2/Peru_strikes.cvx). Compare these to your map and update your interpretation as necessary. 4.) To complete your map, you will need to supplement these strike and dip measurements with your own. Use the Gocad project to calculate strikes and dips for the large southern structure along this line (using the

wizard, which is called “orpick.wz” in the Lab1 folder). Draw these strike and dip measurements on your map. 5.) Do any of the anticlines have 4-way closure (i.e., are they doubly plunging)?

Part 2: Construct a cross section using the kink method 1.) Management agreed to send a barge up the river and drill a test borehole to constrain the stratigraphy of the area. To complete your report to management, you need to create a cross section along A-A’ to illustrate the subsurface geology and to support your argument that this is a worthy prospect. Using the strike and dip data collected in the field, the data that you collected from the satellite images, the borehole data, and the kink method, construct a reasonable cross section. Conclusions 1. Given what you’ve learned about the geology of the area, mark regions on your map that you would recommend for your company to drill a well. If you chose more than one region, indicate which region you think is the best prospect. Explain why:

2. What additional piece of information would help you construct a cross section with more confidence?

3. Your company decided to collect a seismic reflection profile in your area. Where were your interpretations similar? Where were they different? What are some causes of the differences?

To turn in: Your kink method exercise, your Peru map, Peru cross section, and this lab, with all the answers filled in!