Petroleum Geology & Reservoir Characterization Flashcards

In a delta system, which depositional environment typically produces the best reservoir quality sand due to high-energy reworking?

Answer: Distributary mouth bar

Distributary mouth bars are reworked by wave and current energy as river sediment enters the basin, producing well-sorted, clean sands with excellent reservoir quality.

The concept of 'effective porosity' differs from 'total porosity' in that it excludes:

Answer: Clay-bound water and isolated pores

Effective porosity excludes clay-bound water and isolated (non-connected) pore space, representing only the porosity available for fluid flow.

Which tectonic setting is MOST favorable for the formation of foreland basin petroleum systems?

Answer: Continental collision and thrust belt systems

Foreland basins form in front of thrust belts during continental collision, providing thick sedimentary sequences with good source, reservoir, and seal combinations.

What does a negative acoustic impedance contrast at a reservoir boundary indicate on a seismic section?

Answer: Velocity and/or density decrease downward across the boundary

A negative acoustic impedance contrast means the product of velocity and density decreases across the boundary downward, producing a phase reversal in the reflected seismic wavelet.

The Laramide Orogeny is important for Rocky Mountain petroleum geology because it:

Answer: Formed structural traps through basement-involved reverse faulting and folding

The Laramide Orogeny created basement-cored uplifts and adjacent basins through thick-skinned reverse faulting, forming the structural traps that host many Rocky Mountain oil and gas fields.

In carbonate reservoirs, which diagenetic process creates the highest permeability enhancement?

Answer: Dissolution creating vuggy and cavernous porosity

Dissolution of carbonate minerals creates vugs, caverns, and moldic porosity that can dramatically increase both porosity and permeability, creating the best carbonate reservoir quality.

The 'critical gas saturation' in a reservoir refers to:

Answer: The minimum gas saturation at which gas begins to flow as a continuous phase

Critical gas saturation is the minimum gas saturation required for gas to form a continuous phase and begin flowing; below this threshold, gas exists as isolated bubbles that do not migrate.