SPE Reservoir Characterization 3 — Questions and Answers
Question 1: What is the Archie equation primarily used to calculate in petrophysics?
- Formation compressibility from sonic logs
- Water saturation from resistivity and porosity measurements (Correct answer)
- Gas-oil ratio from production logging
- Net pay thickness from gamma ray cutoffs
Correct answer: Water saturation from resistivity and porosity measurements
Archie's law relates formation resistivity, porosity, and water resistivity to calculate water saturation (Sw) in clean formations.
Question 2: In geostatistical reservoir modeling, what is the key difference between Sequential Gaussian Simulation (SGS) and Kriging?
- SGS produces multiple equiprobable realizations while Kriging produces a single smooth best-estimate (Correct answer)
- Kriging honors well data while SGS does not
- SGS only applies to categorical variables while Kriging applies to continuous variables
- Kriging requires variogram analysis while SGS does not
Correct answer: SGS produces multiple equiprobable realizations while Kriging produces a single smooth best-estimate
SGS generates stochastic realizations that honor data and reproduce variogram statistics, whereas Kriging produces a unique smoothed estimate that under-represents heterogeneity.
Question 3: Which core analysis technique directly measures the three-dimensional pore network geometry without destroying the sample?
- Routine core analysis (RCA)
- Micro-CT scanning (Correct answer)
- Dean-Stark extraction
- Soxhlet extraction
Correct answer: Micro-CT scanning
Micro-CT (computed tomography) scanning creates 3D images of pore space at micron resolution without altering the sample.
Question 4: What is the primary driving force for fluid flow in a petroleum reservoir according to Darcy's Law?
- Fluid density contrast
- Pressure gradient (Correct answer)
- Temperature gradient
- Capillary pressure
Correct answer: Pressure gradient
Darcy's Law states that flow rate is proportional to the pressure gradient across a porous medium, adjusted for fluid viscosity and rock permeability.
Question 5: In a carbonate reservoir, which diagenetic process most commonly creates secondary porosity after deposition?
- Compaction of aragonite grains
- Dolomitization and dissolution (karstification) (Correct answer)
- Clay mineral precipitation from formation water
- Silica cementation of pore throats
Correct answer: Dolomitization and dissolution (karstification)
Dolomitization replaces calcite with smaller dolomite crystals, creating intercrystalline pores, while dissolution creates vugs and fractures in carbonates.
Question 6: What does the 'net-to-gross' (NTG) ratio represent in reservoir description?
- The ratio of recoverable reserves to original oil in place
- The proportion of the gross reservoir interval that meets minimum petrophysical cutoffs for pay (Correct answer)
- The ratio of horizontal to vertical permeability
- The fraction of reservoir under structural closure
Correct answer: The proportion of the gross reservoir interval that meets minimum petrophysical cutoffs for pay
Net-to-gross is the ratio of net pay thickness (meeting porosity/saturation/permeability cutoffs) to the total gross reservoir interval thickness.
Question 7: Which seismic attribute is most sensitive to changes in fluid content within reservoir sands?
- Coherence (similarity)
- Acoustic impedance inversion
- Amplitude versus Offset (AVO) anomaly (Correct answer)
- Dip azimuth
Correct answer: Amplitude versus Offset (AVO) anomaly
AVO analysis exploits the variation of seismic amplitude with source-receiver offset, which is sensitive to fluid type (gas vs. brine) and lithology.
SPE Reservoir Characterization 3
What is the Archie equation primarily used to calculate in petrophysics?