Drilling Engineering Principles Flashcards

What is the main advantage of using an oil-based mud (OBM) over a water-based mud (WBM) in certain formations?

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.

What does 'rotary steerable system' (RSS) provide that conventional mud motors cannot?

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.

The 'kick tolerance' of a well is defined as:

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.

Which casing string is primarily designed to protect freshwater aquifers and support the wellhead?

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.

In the context of MWD/LWD tools, what is 'gamma ray' logging primarily used for while drilling?

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.

What is 'lost circulation' in drilling, and what is one common treatment?

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.

What is the 'driller's method' for well control?

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.