CPG Petroleum Geology & Reservoir Characterization 3 — Questions and Answers
Question 1: The Buckley-Leverett equation is used in reservoir engineering to describe:
- Pressure transient behavior in fractured reservoirs
- Immiscible two-phase fluid displacement in porous media (Correct answer)
- Geomechanical compaction of reservoir rocks
- Capillary pressure as a function of saturation
Correct answer: Immiscible two-phase fluid displacement in porous media
The Buckley-Leverett equation describes the fractional flow and frontal advance of an immiscible displacing fluid (e.g., water) through a porous medium.
Question 2: Which structural trap type is formed by the intersection of two normal fault systems creating a down-dropped central block?
- Horst block
- Half-graben
- Graben (Correct answer)
- Rollover anticline
Correct answer: Graben
A graben is a down-dropped crustal block bounded by normal faults on both sides, formed where two normal fault systems intersect or parallel each other.
Question 3: In a type II kerogen, what is the primary hydrocarbon product generated during peak thermal maturation?
- Dry gas only
- Mixed oil and gas (waxy crude)
- Oil-prone hydrocarbons (Correct answer)
- Inert residue (inertinite)
Correct answer: Oil-prone hydrocarbons
Type II kerogen is primarily marine-derived and oil-prone, generating liquid hydrocarbons at peak maturation within the oil window (Ro ~0.6–1.3%).
Question 4: Permeability anisotropy in clastic reservoirs is MOST commonly caused by:
- Tectonic fracturing during burial
- Preferential alignment of clay minerals and bedding lamination (Correct answer)
- Dissolution of evaporite beds
- Dolomitization of carbonate interbeds
Correct answer: Preferential alignment of clay minerals and bedding lamination
Bedding-parallel lamination and aligned clay minerals create higher horizontal permeability than vertical permeability, making permeability anisotropy common in clastic reservoirs.
Question 5: The depth to the gas-water contact in a reservoir is controlled by:
- The spill point of the structural trap (Correct answer)
- Capillary entry pressure of the reservoir rock
- The depth of the source rock
- Regional hydrodynamic flow gradients
Correct answer: The spill point of the structural trap
The gas-water contact is ultimately constrained by the spill point of the structural or stratigraphic trap, below which hydrocarbons cannot be retained.
Question 6: Which seismic attribute is MOST useful for detecting stratigraphic traps associated with channel sand bodies?
- Acoustic impedance inversion
- Coherence/similarity attribute (Correct answer)
- Root mean square (RMS) amplitude
- Instantaneous frequency
Correct answer: Coherence/similarity attribute
Coherence/similarity attributes highlight discontinuities in seismic reflectors, making them ideal for mapping channel edges, faults, and stratigraphic boundaries.
Question 7: What is the significance of a 'bright spot' anomaly on a seismic section in a clastic reservoir?
- It indicates the presence of evaporite minerals
- It indicates high acoustic impedance contrast from basement rocks
- It may indicate a gas sand with anomalously low acoustic impedance (Correct answer)
- It indicates a zone of high formation water salinity
Correct answer: It may indicate a gas sand with anomalously low acoustic impedance
A bright spot is a high-amplitude seismic anomaly often caused by gas-saturated sands, which have significantly lower acoustic impedance than brine-saturated sands or shales.
CPG Petroleum Geology & Reservoir Characterization 3
The Buckley-Leverett equation is used in reservoir engineering to describe: