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Petroleum Geology Assignment 8 Solution...

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Petroleum Geology, Assignment 8 Name: _______________________________________________________ 1. Please refer to the Figure below for a simple anticlinal trap to answer question 1. Out of the different parts of the trap, marked as A, B, C, and D, which one corresponds to the spill-point?

a. A b. B c. C d. D 2. Out of the two traps, marked below as Trap A and Trap B, which one has higher net-to-gross ratio?

a. Trap A b. Trap B 3. For anticlinal traps, its closure is always the same as its structural relief. a. True b. False 4. Please refer to the Figure below and the associated hydrocarbon traps on top of the oil-water contact (OWC). How would you classify these traps?

a. Diapiric traps b. Stratigraphic traps c. Structural (fault) traps d. Combination traps 5. What kind of hydrocarbon trap is shown in the Figure below?

a. Structural trap b. Hydrodynamic trap c. Structural trap d. None of the above 6. A tilted fluid contact can be caused by (choose all that are correct) a. Hydrodynamic flow b. Production from an adjacent field c. Presence of tar mat d. Cementation e. Change in facies 7. Rim-syncline and turtle-back structures can be found around what kind of hydrocarbon traps? a. Structural traps b. Diapiric traps c. Stratigraphic traps d. Hydrodynamic traps 8. What kind of trap is indicated by the Figure below?

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a. Structural (anticlinal) trap b. Structural (fault) trap c. Stratigraphic (pinchout) trap d. Diapiric trap 9. What type of hydrocarbon trap is depicted by the following Figure?

a. Stratigraphic (pinchout) trap b. Stratigraphic (diagenetic) trap c. Stratigraphic (unconformity-related) trap d. None of the above 10. The Figure below shows a simplified cross-section from an oilfield there the hydrocarbon is trapped partly in the sands, partly in the reefal carbonates, and partly from the fractured and weathered granite. How would you classify this trap to be?

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a. Structural trap b. Stratigraphic (subunconformity) trap c. Stratigraphic (supraunconformity) trap d. Diapiric trap 11. The Figure below is the geological cross-section of an oil and gas field from the Niger delta. As what kind of hydrocarbon trap would you classify it? a. Structural (fault) trap b. Structural (anticlinal) trap c. Stratigraphic (pinchout) trap d. Combination trap

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12. The Figure below is a geological cross-section showing hydrocarbon accumulations shown as the areas shaded in black (A-F). As what kind of trap would you classify them to be? a. Structural trap b. Hydrodynamic trap c. Combination trap d. Diapiric trap e. None of the above

13. Regarding the same Figure (above) what is the structure of the trap E is usually called? a. Simple anticline b. Turtle-back structure 5

c. Fault d. Pinchout e. None of the above 14. Are the hydrocarbon traps resulting from the mud diapirs analogous to the ones from the salt diapirs? a. Yes b. No 15. The Figure below shows a sand layer enclosed in an impermeable shale with hydrocarbon accumulations shaded in black.

How would you classify this trap? a. A structural (anticlinal) trap. b. A stratigraphic (diagenetic) trap. c. A structural (fault) trap. d. A stratigraphic (pinchout) trap. 16. The Figure below and the associated hydrocarbon trapped on top of the oil water contact (OWC) is a simplified geological cross-section of the Forties field, North Sea. The major feature of this field is the horst and graben structures in the basement rocks and the associated structures in the overlying sediments generating different kinds of traps and one such trap is shown in this Figure.

How would you classify this hydrocarbon trap? 6

a. Diapiric trap. b. Hydrodynamic trap. c. Compactional anticlinal trap. d. Stratigraphic trap. e. Compressional anticlinal trap. 17. The Figure below is an interpreted seismic section from a Canadian oilfield with known deep and shallow reservoirs, indicated by circles.

What is the most likely trapping mechanism for these reservoirs? a. Structural (fault). b. Stratigraphic (pinchout). c. Structural (anticlinal). d. Hydrodynamic. e. Stratigraphic (diagenetic). 18. What kind of trap is represented by the following Figure?

a. b. c. d. e.

Structural (fault). Stratigraphic (pinchout). Structural (anticlinal). Hydrodynamic. Stratigraphic (diagenetic). 7

19. The Figure below shows many hydrocarbon accumulations in the areas shaded in black. That kind of traps are these?

a. Stratigraphic. b. Structural. c. Hydrodynamic. d. Diapiric. 20. The Figure below shows two scenarios of hydrocarbon accumulations in which (a) the porosity and permeability are lost by cementation up-dip, and (b) porosity and permeability are enhanced by dolomitization in an otherwise tight formation.

How would you classify these hydrocarbon traps? a. Structural traps b. Combination traps c. Stratigraphic (diagenetic) traps d. Hydrodynamic traps e. Unconformity-related stratigraphic traps

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21. The Figure below is a geological cross-section from an oil-field showing shale, sand and carbonate deposits.

If hydrocarbon is trapped within the sands, what type of trap would that be? a. Stratigraphic (sub-unconformity) trap b. Hydrodynamic trap c. Stratigraphic (supra- unconformity) trap d. Stratigraphic (diagenetic) trap e. None of the above 22. The Figure below shows a seismic section from the east-Texas. These seismic data were acquired over the Woodbine gas-sand play that terminate below an unconformity whose base is marked by an impermeable shale, underlying the Austin Chalk (see the Figure). Two gas-producing wells (A and B) and two dry (water filled) wells (C and D) drilled through the Woodbine formation are also shown. The location of the Woodbine sand formation at the producing wells A and B are also marked by blue circles.

How would you classify the traps producing from wells A and B? a. Structural trap b. Stratigraphic (sub-unconformity) trap c. Stratigraphic (supra-unconformity) trap d. Combination trap 23. Referring to the Figure related to question 22, in terms of seismic sequence stratigraphy, how would you classify the truncation of the Woodbine sand against the overlying shale? a. Onlap b. Downlap c. Toplap d. Erosional truncation 24. For a reservoir of gross thickness of 50 feet and a net-to-gross ratio of 0.4, what is its net thickness? 9

a. 10 feet b. 20 feet c. 30 feet d. 40 feet e. 50 feet 25. The Figure below is the seismic velocity extracted from data and displayed in a color scale as shown.

What is your interpretation of the zone marked with a question mark? a. The zone is possibly normally pressured. b. The zone is possibly sub-normally pressured. c. The zone is possibly over-pressured d. None of the above.

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