SPE Reservoir Engineering & Management 3 — Questions and Answers
Question 1: Which dimensionless number governs the ratio of viscous to gravity forces during reservoir fluid displacement?
- Capillary number
- Gravity number (Correct answer)
- Reynolds number
- Peclet number
Correct answer: Gravity number
The gravity number (ratio of gravity to viscous forces) determines whether gravity override or underride occurs during immiscible displacement.
Question 2: In a naturally fractured reservoir (Type 1 NFR), the matrix blocks primarily act as:
- Flow conduits to the wellbore
- Storage volumes that feed fluids into fractures (Correct answer)
- Impermeable seals between fractures
- Capillary pressure equilibrators only
Correct answer: Storage volumes that feed fluids into fractures
In Type 1 NFRs, the matrix provides the dominant storage capacity while the fracture network provides flow capacity (permeability) to the wellbore.
Question 3: The Lorenz coefficient is used in reservoir engineering to quantify:
- Fluid viscosity variation with pressure
- Vertical heterogeneity of permeability (Correct answer)
- Horizontal stress anisotropy
- Capillary entry pressure distribution
Correct answer: Vertical heterogeneity of permeability
The Lorenz coefficient (0 = perfectly homogeneous, 1 = perfectly heterogeneous) measures permeability variation across reservoir layers from a flow capacity plot.
Question 4: During secondary recovery by waterflooding, the economic limit is typically reached when:
- Water cut exceeds 5%
- The incremental oil revenue no longer covers lifting costs at prevailing WOR (Correct answer)
- Reservoir pressure drops below bubble point
- Injected water exceeds pore volume
Correct answer: The incremental oil revenue no longer covers lifting costs at prevailing WOR
The economic limit occurs when the value of incremental oil production no longer justifies operating costs, often at very high water-oil ratios.
Question 5: Which EOR method is most suitable for a high-temperature, high-salinity carbonate reservoir with moderate viscosity oil?
- Polymer flooding
- Miscible CO2 injection (Correct answer)
- Steam injection
- Microbial EOR
Correct answer: Miscible CO2 injection
Miscible CO2 injection is effective in carbonates with moderate viscosity oil because CO2 achieves miscibility at attainable pressures and is less sensitive to salinity and temperature than chemical EOR.
Question 6: The concept of 'skin factor' in well testing represents:
- Surface roughness of the wellbore casing
- Additional pressure drop due to near-wellbore damage or stimulation (Correct answer)
- The ratio of gas to oil production rates
- Capillary pressure at the gas-water contact
Correct answer: Additional pressure drop due to near-wellbore damage or stimulation
Skin factor (S) quantifies the extra pressure drop caused by near-wellbore damage (positive S) or stimulation such as hydraulic fracturing (negative S).
Question 7: Interporosity flow coefficient (λ) in dual-porosity models describes:
- The ratio of fracture volume to total pore volume
- The fluid transfer rate between matrix and fractures (Correct answer)
- Wellbore storage during early transient flow
- The anisotropy of horizontal permeability
Correct answer: The fluid transfer rate between matrix and fractures
Lambda (λ) characterizes how easily fluid transfers from matrix blocks into the fracture network, controlling the transition period on pressure transient plots.
SPE Reservoir Engineering & Management 3
Which dimensionless number governs the ratio of viscous to gravity forces during reservoir fluid displacement?