CPG Research Methods & Evidence-Based Practice 3 — Questions and Answers
Question 1: A petroleum geologist is comparing two competing structural interpretations of the same seismic dataset. The most rigorous evidence-based approach is to:
- Select the interpretation that yields the largest prospect
- Choose the interpretation made by the most senior geologist
- Test both interpretations against all available well and production data and quantify uncertainty (Correct answer)
- Accept the first interpretation to save time
Correct answer: Test both interpretations against all available well and production data and quantify uncertainty
Testing competing interpretations against all hard data and expressing residual uncertainty is the hallmark of rigorous evidence-based subsurface analysis.
Question 2: What is the primary purpose of using a type well or type log in regional stratigraphic research?
- To serve as a legal reference for mineral rights disputes
- To establish a standard reference section for correlation across the study area (Correct answer)
- To define the economic cutoff for pay intervals
- To calibrate the drilling rate of penetration
Correct answer: To establish a standard reference section for correlation across the study area
A type well provides a reference log section that defines stratigraphic nomenclature and serves as the correlation standard for the region.
Question 3: In petrophysical research, which quality control step is essential before using wireline logs for quantitative analysis?
- Converting all logs to metric units
- Environmental corrections for borehole conditions (Correct answer)
- Removing all data below the oil-water contact
- Converting resistivity to acoustic impedance
Correct answer: Environmental corrections for borehole conditions
Environmental corrections account for borehole diameter, mud type, temperature, and pressure effects that distort raw log measurements.
Question 4: Which approach best reduces interpreter subjectivity when picking formation tops across hundreds of wells?
- Assigning each interpreter a different zone to pick independently without review
- Using a single interpreter for all picks without peer review
- Establishing standardized picking criteria and conducting blind inter-rater consistency checks (Correct answer)
- Picking tops solely from gamma ray logs ignoring other curves
Correct answer: Establishing standardized picking criteria and conducting blind inter-rater consistency checks
Standardized criteria combined with inter-rater reliability testing minimizes subjective variability in stratigraphic picks.
Question 5: When a geologist uses outcrop analogues to constrain subsurface reservoir architecture, which limitation must always be acknowledged?
- Outcrops cannot be measured accurately
- Diagenetic overprinting and erosional modification may have altered the original reservoir geometry (Correct answer)
- Analogues are only valid in the same geological age
- Outcrop data cannot be digitized
Correct answer: Diagenetic overprinting and erosional modification may have altered the original reservoir geometry
Outcrops may have experienced weathering, erosion, or diagenetic changes that make direct quantitative transfer to subsurface conditions problematic.
Question 6: A bootstrap resampling technique in petroleum statistics is used primarily to:
- Simulate fluid flow in a reservoir model
- Estimate the uncertainty in a statistical parameter when the underlying distribution is unknown (Correct answer)
- Calculate the net-to-gross ratio from core data
- Convert depth to time in seismic interpretation
Correct answer: Estimate the uncertainty in a statistical parameter when the underlying distribution is unknown
Bootstrap resampling generates an empirical distribution by repeatedly sampling with replacement, enabling uncertainty estimation without assuming a parametric distribution.
Question 7: In evidence-based petroleum geoscience, a 'null hypothesis' regarding reservoir connectivity would state that:
- All reservoir compartments are fully connected
- There is no hydraulic connection between defined compartments until data prove otherwise (Correct answer)
- The reservoir is dry until proven productive
- Production data always confirm geological models
Correct answer: There is no hydraulic connection between defined compartments until data prove otherwise
The null hypothesis assumes no effect or no connection exists; the burden of proof lies with demonstrating connectivity through pressure tests or production data.
CPG Research Methods & Evidence-Based Practice 3
A petroleum geologist is comparing two competing structural interpretations of the same seismic dataset.
The most rigorous evidence-based approach is to: