CPG Drilling Operations & Well Logging 3 — Questions and Answers
Question 1: What is the function of a blowout preventer (BOP) annular preventer compared to a ram preventer?
- Annular preventers seal only around drill pipe; ram preventers seal any wellbore geometry
- Annular preventers use rubber elements to seal around any pipe size or open hole; rams seal specific pipe sizes or close the bore (Correct answer)
- Both perform identical sealing functions
- Annular preventers are only used offshore; rams are used onshore
Correct answer: Annular preventers use rubber elements to seal around any pipe size or open hole; rams seal specific pipe sizes or close the bore
Annular BOPs use a flexible rubber element that can close around various pipe sizes or open hole, while ram BOPs use steel rams configured for specific pipe diameters or blind/shear closure.
Question 2: On a resistivity log, a hydrocarbon-bearing zone typically shows:
- Low resistivity similar to surrounding shales
- Very high resistivity compared to water-saturated zones (Correct answer)
- Negative resistivity values
- Resistivity equal to formation water
Correct answer: Very high resistivity compared to water-saturated zones
Hydrocarbons are non-conductive, so hydrocarbon-bearing formations exhibit significantly higher resistivity than water-saturated zones of the same lithology.
Question 3: Which cement job design consideration is most critical for preventing sustained casing pressure (SCP)?
- Using the highest pump rate possible
- Ensuring a continuous, void-free cement sheath from the shoe to above the target zone (Correct answer)
- Minimizing the cement slurry density
- Keeping cement setting time under 2 hours
Correct answer: Ensuring a continuous, void-free cement sheath from the shoe to above the target zone
SCP (sustained casing pressure) results from gas migration through incomplete cement sheaths; a continuous, void-free cement column isolates formation fluids from the annulus.
Question 4: A drill string becomes differentially stuck. The correct first remedial action is usually to:
- Increase rotary speed to free the pipe
- Apply maximum overpull to break the pipe free
- Reduce mud weight and spot a freeing agent (spotting pill) across the stuck point (Correct answer)
- Cement in place and sidetrack
Correct answer: Reduce mud weight and spot a freeing agent (spotting pill) across the stuck point
Differential sticking results from the pressure differential holding the pipe against the filter cake; reducing this differential and lubricating the contact area with a spotting pill is the standard first response.
Question 5: What is the purpose of the 'formation integrity test' (FIT) or 'leak-off test' (LOT) performed after setting casing?
- To measure reservoir permeability
- To determine the maximum drilling fluid weight the formation can withstand without fracturing (Correct answer)
- To evaluate cement bond quality
- To measure the temperature gradient in the wellbore
Correct answer: To determine the maximum drilling fluid weight the formation can withstand without fracturing
LOT/FIT pressurizes the open-hole section below the casing shoe to establish the maximum mud weight that can be safely used before the formation fractures.
Question 6: In directional drilling, the 'build rate' refers to:
- Rate of penetration in deviated wellbores
- Rate of increase in wellbore inclination angle (degrees per 100 ft) (Correct answer)
- The speed at which torque builds in the string
- The increase in mud weight required per 1,000 ft of depth
Correct answer: Rate of increase in wellbore inclination angle (degrees per 100 ft)
Build rate describes how quickly the wellbore inclination increases, typically expressed as degrees per 100 feet, and is a key parameter in directional well planning.
Question 7: A caliper log showing a consistently larger borehole diameter than bit size most likely indicates:
- Compressive failure creating borehole breakout
- Borehole washout due to weak or water-sensitive formations (Correct answer)
- Presence of a hydrocarbon reservoir
- Tight, over-pressured shale
Correct answer: Borehole washout due to weak or water-sensitive formations
Washout occurs when drilling fluid erodes or disaggregates weak, unconsolidated, or water-sensitive (swelling clay) formations, producing a borehole larger than the bit diameter.
CPG Drilling Operations & Well Logging 3
What is the function of a blowout preventer (BOP) annular preventer compared to a ram preventer?