CPG Case Analysis & Practical Application 2 — Questions and Answers
Question 1: A wildcat well encounters unexpected overpressure at 10,000 ft in a shale sequence. What is the most likely cause?
- Hydrocarbon generation and fluid expansion in a sealed compartment (Correct answer)
- Normal compaction disequilibrium only
- Tectonic uplift reducing overburden
- Diagenetic cementation reducing porosity
Correct answer: Hydrocarbon generation and fluid expansion in a sealed compartment
Overpressure in sealed shale sequences at depth is most commonly caused by hydrocarbon generation creating fluid expansion within a pressure compartment.
Question 2: A prospect has four-way dip closure but seismic amplitude anomalies are absent. Which interpretation is most appropriate?
- The trap may contain brine or tight rock rather than commercial hydrocarbons (Correct answer)
- The prospect is definitively dry
- Amplitude anomalies are required for any valid prospect
- The closure indicates a confirmed structural trap with hydrocarbons
Correct answer: The trap may contain brine or tight rock rather than commercial hydrocarbons
Absence of amplitude anomalies in a structurally closed trap suggests either water-saturated reservoir or tight rock with insufficient impedance contrast.
Question 3: During field appraisal, two wells on opposite flanks of an anticline both show oil-water contacts at different depths. What does this most likely indicate?
- Multiple reservoir compartments separated by a permeability barrier or fault (Correct answer)
- Measurement error in both wells
- A single aquifer with tilted contact due to hydrodynamics
- Fault seal failure
Correct answer: Multiple reservoir compartments separated by a permeability barrier or fault
Different OWC depths on opposite flanks typically indicate compartmentalization caused by faults or stratigraphic barriers separating the reservoir.
Question 4: A geologist is evaluating a turbidite channel play. The best analog to constrain net-to-gross ratio would be:
- Outcrop studies of exhumed turbidite systems with similar depositional setting (Correct answer)
- Regional seismic amplitude maps only
- Nearby fluvial channel wells
- Global average sandstone net-to-gross of 60%
Correct answer: Outcrop studies of exhumed turbidite systems with similar depositional setting
Outcrop analogs from comparable turbidite systems provide the most direct constraints on architecture, net-to-gross, and connectivity.
Question 5: A production well shows rapid water breakthrough only 6 months after first oil. The most diagnostic first step is to:
- Run a water tracer test or analyze water chemistry to identify the water source (Correct answer)
- Immediately perforate an upper interval
- Shut the well in permanently
- Increase pump rate to outpace water influx
Correct answer: Run a water tracer test or analyze water chemistry to identify the water source
Identifying whether breakthrough is from the aquifer, injector, or a behind-pipe zone requires chemical fingerprinting or tracer analysis before any remediation.
Question 6: An operator is deciding whether to drill a development well based on a P50 EUR of 300 MBOE. The well cost is $4M and oil price is $60/bbl. Which additional factor is most critical to assess economic viability?
- Operating costs, royalties, and the production decline curve shape (Correct answer)
- Surface elevation of the drill site
- Color of oil (API gravity alone)
- Distance to the nearest pipeline without considering tariff
Correct answer: Operating costs, royalties, and the production decline curve shape
EUR alone does not determine profitability; operating costs, royalty burden, and the time-shape of production (decline curve) all drive NPV.
Question 7: A CPG is peer-reviewing a volumetric calculation and notices the team used an area measurement from an un-depth-converted time map. What is the primary risk?
- Lateral velocity variations will distort structural geometry and lead to erroneous area estimates (Correct answer)
- The calculation is acceptable if the field is shallow
- Time maps always overestimate area
- Depth conversion only affects thickness, not area
Correct answer: Lateral velocity variations will distort structural geometry and lead to erroneous area estimates
Lateral velocity heterogeneity causes time-to-depth conversion to alter both the shape and area of structural closures, not just thickness.
CPG Case Analysis & Practical Application 2
A wildcat well encounters unexpected overpressure at 10,000 ft in a shale sequence.
What is the most likely cause?