SPE Reservoir Engineering & Management 2 — Questions and Answers
Question 1: Which drive mechanism typically yields the highest primary recovery factor in oil reservoirs?
- Solution gas drive
- Water drive (Correct answer)
- Gas cap drive
- Gravity drainage
Correct answer: Water drive
Water drive reservoirs typically achieve the highest primary recovery (40–60%) because water maintains reservoir pressure more effectively than other mechanisms.
Question 2: The van Everdingen-Hurst aquifer model is used primarily to calculate:
- Cumulative water influx into a reservoir (Correct answer)
- Wellbore skin damage
- Capillary pressure curves
- Gas compressibility factor
Correct answer: Cumulative water influx into a reservoir
The van Everdingen-Hurst model provides transient aquifer influx calculations using dimensionless time and influx functions.
Question 3: In a gas reservoir, the z-factor (gas compressibility factor) is determined as a function of:
- Temperature and porosity
- Pseudo-reduced pressure and pseudo-reduced temperature (Correct answer)
- Permeability and skin factor
- Water saturation and capillary pressure
Correct answer: Pseudo-reduced pressure and pseudo-reduced temperature
The z-factor is obtained from correlations (e.g., Standing-Katz chart) using pseudo-reduced pressure and temperature derived from gas composition.
Question 4: Buckley-Leverett theory predicts the frontal advance rate of a displacing fluid by applying:
- Darcy's law alone
- The fractional flow equation and continuity equation (Correct answer)
- Capillary pressure curves only
- Steady-state relative permeability
Correct answer: The fractional flow equation and continuity equation
Buckley-Leverett combines the fractional flow equation with the continuity equation to predict saturation profile movement during immiscible displacement.
Question 5: A reservoir's areal sweep efficiency in a waterflood is most directly improved by:
- Increasing injection rate indefinitely
- Optimizing well pattern geometry and infill drilling (Correct answer)
- Reducing produced water handling capacity
- Lowering reservoir temperature
Correct answer: Optimizing well pattern geometry and infill drilling
Optimizing injector/producer well patterns (e.g., five-spot, inverted nine-spot) and adding infill wells directly improves areal sweep of the flood.
Question 6: Which equation is used to calculate original oil in place (OOIP) using the volumetric method?
- N = 7758 × A × h × φ × (1 - Sw) / Boi (Correct answer)
- N = q × Bt / (ΔP × ct)
- N = Np × Bo + Wp × Bw - We
- N = (Pi - P) / (ct × Pi)
Correct answer: N = 7758 × A × h × φ × (1 - Sw) / Boi
The volumetric OOIP formula multiplies the reservoir bulk volume (7758 × A × h), net-to-gross porosity, and hydrocarbon saturation, divided by the initial oil FVF.
Question 7: What is the primary purpose of a pressure transient test (e.g., buildup test) in reservoir engineering?
- Measure surface oil gravity
- Determine reservoir permeability, skin, and boundaries (Correct answer)
- Calibrate stock tank volumes
- Quantify wellbore cement integrity
Correct answer: Determine reservoir permeability, skin, and boundaries
Pressure buildup tests analyze wellbore pressure recovery after shut-in to determine near-well permeability, skin damage, and detect reservoir boundaries.
SPE Reservoir Engineering & Management 2
Which drive mechanism typically yields the highest primary recovery factor in oil reservoirs?