SPE Drilling Engineering Principles 3 — Questions and Answers
Question 1: What is the main advantage of using an oil-based mud (OBM) over a water-based mud (WBM) in certain formations?
- OBM is less expensive to prepare
- OBM inhibits clay swelling and provides better wellbore stability in reactive shales (Correct answer)
- OBM increases rate of penetration in hard rock
- OBM requires less weighting material
Correct answer: OBM inhibits clay swelling and provides better wellbore stability in reactive shales
Oil-based muds are highly inhibitive to clay hydration and swelling, making them ideal for drilling through water-sensitive shale formations that would otherwise cause wellbore instability.
Question 2: What does 'rotary steerable system' (RSS) provide that conventional mud motors cannot?
- Higher weight on bit capability
- Continuous rotation of the drill string while steering the wellbore (Correct answer)
- Improved cement bond between casing and formation
- Reduced mud weight requirements
Correct answer: Continuous rotation of the drill string while steering the wellbore
RSS allows continuous rotation of the entire drill string while simultaneously steering the well, unlike mud motors which require sliding (non-rotating) mode for directional changes.
Question 3: The 'kick tolerance' of a well is defined as:
- The maximum pump rate before the well kicks
- The maximum influx volume that can be safely shut in and circulated out without fracturing the weakest exposed formation (Correct answer)
- The difference between mud weight and formation pressure
- The time allowed between kick detection and BOP closure
Correct answer: The maximum influx volume that can be safely shut in and circulated out without fracturing the weakest exposed formation
Kick tolerance is the maximum kick volume that can be safely handled given the current mud weight and the fracture gradient of the weakest exposed formation.
Question 4: Which casing string is primarily designed to protect freshwater aquifers and support the wellhead?
- Production casing
- Intermediate casing
- Surface casing (Correct answer)
- Liner
Correct answer: Surface casing
Surface casing is set to protect freshwater aquifers from contamination, support the wellhead and BOP stack, and provide structural integrity for shallower operations.
Question 5: In the context of MWD/LWD tools, what is 'gamma ray' logging primarily used for while drilling?
- Measuring bottomhole pressure
- Identifying shale versus sand formations by detecting natural radioactivity (Correct answer)
- Measuring the diameter of the wellbore
- Evaluating cement quality behind casing
Correct answer: Identifying shale versus sand formations by detecting natural radioactivity
Gamma ray logs detect natural radioactivity from potassium, uranium, and thorium in formations, with shales showing high GR values and clean sands showing low values.
Question 6: What is 'lost circulation' in drilling, and what is one common treatment?
- Loss of drilling fluid into permeable or fractured formations; treated with lost circulation materials (LCM) (Correct answer)
- Loss of drill bits in the wellbore; treated by fishing operations
- Loss of wellbore pressure; treated by increasing mud weight
- Loss of directional control; treated by re-running surveys
Correct answer: Loss of drilling fluid into permeable or fractured formations; treated with lost circulation materials (LCM)
Lost circulation occurs when drilling fluid flows into natural or induced fractures or vugular formations; LCM such as fibers, flakes, or granules are pumped to plug the thief zone.
Question 7: What is the 'driller's method' for well control?
- Using a computer to calculate the required kill mud weight
- Circulating the kick out with original mud weight first, then circulating kill-weight mud in a second circulation (Correct answer)
- Pumping kill-weight mud directly to the bit in a single circulation
- Bullheading the kick back into the formation
Correct answer: Circulating the kick out with original mud weight first, then circulating kill-weight mud in a second circulation
The driller's method uses two separate circulations: the first removes the influx using original mud weight, and the second displaces the wellbore with kill-weight mud.
SPE Drilling Engineering Principles 3
What is the main advantage of using an oil-based mud (OBM) over a water-based mud (WBM) in certain formations?