SPE Reservoir Characterization 2 — Questions and Answers
Question 1: Which petrophysical parameter is defined as the ratio of pore volume to total bulk volume of a rock sample?
- Permeability
- Porosity (Correct answer)
- Saturation
- Compressibility
Correct answer: Porosity
Porosity is the ratio of pore volume to bulk volume, expressed as a fraction or percentage.
Question 2: In a water-wet reservoir, where does water preferentially reside?
- Center of pore throats
- Contact with grain surfaces (Correct answer)
- Gas cap zone
- Top of the reservoir
Correct answer: Contact with grain surfaces
In water-wet systems, water coats grain surfaces and occupies smaller pore spaces due to its affinity for the rock.
Question 3: What does the term 'irreducible water saturation' (Swi) represent in reservoir engineering?
- The maximum water saturation achievable by waterflooding
- The minimum water saturation that cannot be displaced by hydrocarbons (Correct answer)
- The average water saturation in the transition zone
- The water saturation at the free water level
Correct answer: The minimum water saturation that cannot be displaced by hydrocarbons
Irreducible water saturation is the minimum water held by capillary and adsorptive forces that cannot be displaced by oil or gas.
Question 4: Which log is most commonly used to identify lithology changes and correlate stratigraphic units across wells?
- Neutron porosity log
- Gamma ray log (Correct answer)
- Resistivity log
- Sonic log
Correct answer: Gamma ray log
The gamma ray log measures natural radioactivity, distinguishing shales (high GR) from clean sands or carbonates (low GR) for lithology and correlation.
Question 5: What is the primary purpose of a repeat formation tester (RFT) or modular dynamic tester (MDT) in well logging?
- Measure formation temperature gradient
- Obtain downhole fluid samples and pressure measurements at discrete depths (Correct answer)
- Determine the mechanical strength of the formation
- Evaluate cement bond quality behind casing
Correct answer: Obtain downhole fluid samples and pressure measurements at discrete depths
RFT/MDT tools set packers to seal off intervals, measure formation pressure, and collect representative fluid samples at multiple depths.
Question 6: In reservoir characterization, what does 'facies' refer to?
- The geometric shape of a reservoir trap
- A body of rock with defined characteristics reflecting its depositional environment (Correct answer)
- The pressure compartments within a reservoir
- The fluid contacts identified on logs
Correct answer: A body of rock with defined characteristics reflecting its depositional environment
A facies is a distinctive rock unit defined by its lithology, texture, fossils, or sedimentary structures that reflects a specific depositional environment.
Question 7: Which method uses the relationship between capillary pressure and fluid saturation to estimate reservoir rock quality and pore structure?
- Dean-Stark extraction
- Mercury injection capillary pressure (MICP) analysis (Correct answer)
- X-ray diffraction (XRD)
- Thin section petrography
Correct answer: Mercury injection capillary pressure (MICP) analysis
MICP forces mercury into core plugs at increasing pressures, revealing pore throat size distribution and capillary entry pressures.
SPE Reservoir Characterization 2
Which petrophysical parameter is defined as the ratio of pore volume to total bulk volume of a rock sample?