CMM Exploration & Production Processes 4 — Questions and Answers
Question 1: What distinguishes unconventional reservoirs (e.g., shale gas, tight oil) from conventional reservoirs?
- They are located offshore rather than onshore
- They have very low permeability requiring stimulation to produce economically (Correct answer)
- They contain heavier oil grades
- They are found at shallower depths
Correct answer: They have very low permeability requiring stimulation to produce economically
Unconventional reservoirs have nano-darcy to micro-darcy permeability and require horizontal drilling and hydraulic fracturing to achieve commercial flow rates.
Question 2: Which pressure regime is said to exist when formation pressure exceeds normal hydrostatic gradient and can cause well control challenges?
- Subnormal pressure
- Overpressure (geopressure) (Correct answer)
- Atmospheric pressure
- Hydrostatic equilibrium
Correct answer: Overpressure (geopressure)
Overpressured (geopressured) zones have pore pressures above normal hydrostatic, increasing blowout risk if mud weight is insufficient.
Question 3: In a gas reservoir using material balance, what is the primary data required to estimate original gas in place (OGIP) using the p/z method?
- Production rates and wellbore diameter
- Reservoir pressure and cumulative gas production over time (Correct answer)
- Formation water salinity and temperature
- Seismic amplitude and porosity logs
Correct answer: Reservoir pressure and cumulative gas production over time
The p/z method plots p/z versus cumulative gas production; extrapolation to p/z = 0 gives OGIP for a volumetric gas reservoir.
Question 4: Which completion method involves isolating production zones using inflatable or swellable packers to selectively fracture multiple intervals in a horizontal well?
- Single-zone open-hole completion
- Multistage hydraulic fracturing completion (Correct answer)
- Natural flow completion without stimulation
- Gravel pack completion
Correct answer: Multistage hydraulic fracturing completion
Multistage fracturing uses packers to isolate clusters or stages along the lateral, enabling sequential hydraulic fracturing of each interval.
Question 5: What is the function of a subsurface safety valve (SSSV) in a production well?
- To regulate surface production rates
- To automatically shut in the well downhole if surface conditions indicate a loss of control (Correct answer)
- To measure downhole pressure continuously
- To separate gas from liquid at depth
Correct answer: To automatically shut in the well downhole if surface conditions indicate a loss of control
The SSSV is a fail-safe device set below the wellhead that closes automatically if surface pressure or control line pressure is lost.
Question 6: Which drilling hazard is characterized by the drill string becoming stuck due to differential pressure pinning it against a permeable formation?
- Hole collapse or wellbore instability
- Differential sticking (Correct answer)
- Lost circulation
- Bit balling
Correct answer: Differential sticking
Differential sticking occurs when the pressure difference between the wellbore and a permeable formation pushes the drill string against the filter cake, embedding it.
Question 7: What is the purpose of an extended well test (EWT) conducted before full field development?
- To permanently produce the reservoir to sales
- To evaluate reservoir performance, fluid properties, and flow rates over an extended period (Correct answer)
- To test casing integrity only
- To measure surface facility capacity
Correct answer: To evaluate reservoir performance, fluid properties, and flow rates over an extended period
An EWT provides long-duration dynamic reservoir data including pressure behavior, fluid characterization, and productivity before committing to full development.
CMM Exploration & Production Processes 4
What distinguishes unconventional reservoirs (e.g., shale gas, tight oil) from conventional reservoirs?