CPG CPG Basin Analysis & Structural Geology 1 — Questions and Answers
Question 1: Which type of sedimentary basin forms primarily due to lithospheric extension and thinning?
- Foreland basin
- Rift basin (Correct answer)
- Strike-slip basin
- Peripheral basin
Correct answer: Rift basin
Rift basins form where tectonic extension stretches and thins the crust, creating half-grabens and grabens that fill with sediment.
Question 2: The petroleum system concept requires which of the following essential elements?
- Only source rock and reservoir rock
- Source rock, reservoir rock, trap, seal, and overburden (Correct answer)
- Trap, seal, and migrating fluid only
- Source rock and structural closure
Correct answer: Source rock, reservoir rock, trap, seal, and overburden
A complete petroleum system requires source rock, reservoir rock, trap, seal, and sufficient overburden for maturation, along with the right timing of each.
Question 3: Vitrinite reflectance (%Ro) is used in basin analysis primarily to assess:
- Reservoir porosity
- Thermal maturity of source rocks (Correct answer)
- Fault activity timing
- Depositional environment
Correct answer: Thermal maturity of source rocks
Vitrinite reflectance increases as organic matter is heated over geological time, making it the standard measure of thermal maturity for source rock evaluation.
Question 4: In structural geology, a thrust fault is characterized by:
- Hanging wall moving down relative to footwall
- Hanging wall moving up relative to footwall at low dip angle (Correct answer)
- Vertical displacement with minimal horizontal component
- Lateral displacement parallel to strike
Correct answer: Hanging wall moving up relative to footwall at low dip angle
Thrust faults are reverse faults with dip angles less than 45°, where compression causes the hanging wall to ride up and over the footwall.
Question 5: Which basin type is typically associated with the foreland of fold-and-thrust belts and is loaded by the weight of thrust sheets?
- Rift basin
- Foreland basin (Correct answer)
- Pull-apart basin
- Passive margin basin
Correct answer: Foreland basin
Foreland basins form in front of orogenic belts where the lithosphere flexes downward under the weight of advancing thrust sheets, creating an asymmetric depocenter.
Question 6: The 'oil window' in a sedimentary basin typically corresponds to vitrinite reflectance values of approximately:
- 0.2–0.5% Ro
- 0.6–1.3% Ro (Correct answer)
- 1.5–2.0% Ro
- Greater than 3.0% Ro
Correct answer: 0.6–1.3% Ro
The oil generation window corresponds to %Ro values of approximately 0.6–1.3%, while higher maturities produce wet gas and then dry gas.
CPG CPG Basin Analysis & Structural Geology 1
Which type of sedimentary basin forms primarily due to lithospheric extension and thinning?