CPG Basin Analysis & Structural Geology Flashcards

Strike-slip (wrench) faults most commonly create hydrocarbon traps through which structural mechanism?

Answer: Flower structures and en-echelon folds

Strike-slip faults generate positive and negative flower structures and en-echelon folds along fault bends and stepovers that can form effective traps.

Subsidence analysis (backstripping) in basin analysis is primarily used to:

Answer: Separate tectonic subsidence from sediment loading effects

Backstripping removes the effect of sediment loading to isolate tectonic subsidence, which reveals the basin's driving mechanism and thermal history.

Which kerogen type is most prone to generating oil rather than gas?

Answer: Type II (algal/marine, liptinite-rich)

Type II kerogen, derived from marine algae and plankton, has a high hydrogen index and generates primarily oil at peak maturity.

Structural closure in a four-way dip closure trap is defined as:

Answer: The area enclosed by the lowest closing contour around a structural high

Structural closure is the area enclosed by the lowest structural contour that completely surrounds the closure, limiting the trap's capacity to hold hydrocarbons.

In the context of secondary migration, hydrocarbons move from source rock to trap primarily via:

Answer: Buoyancy-driven flow along carrier beds and faults

Secondary migration occurs as hydrocarbons, being less dense than water, rise buoyantly through permeable carrier beds and along faults until they are trapped.

Unconformity traps rely on which geological relationship to form a seal?

Answer: Truncation of reservoir beds below an impermeable erosional surface

Unconformity traps form where porous reservoir beds are truncated by erosion and then overlain by impermeable rocks, sealing the upslope edge of the reservoir.