Drilling Engineering Principles Flashcards

What does 'torque and drag' analysis evaluate in directional well planning?

Answer: The rotational resistance (torque) and axial friction (drag) forces acting on the drill string in a deviated wellbore

Torque and drag analysis predicts friction forces on the drill string due to wellbore contact, helping engineers design BHAs, select lubricants, and plan well trajectories to avoid operational limits.

In cementing operations, what is a 'lead slurry' versus a 'tail slurry'?

Answer: Lead slurry is a lightweight, high-volume slurry pumped first to fill the upper annulus, while tail slurry is a heavier, stronger slurry placed near the shoe

In a two-stage cement job, the lighter lead slurry fills the upper annulus with less risk of fracturing weak zones, while the denser tail slurry provides strength and zonal isolation near the casing shoe.

What drilling phenomenon is described as 'wellbore breathing' or 'ballooning'?

Answer: The cyclic gain and loss of returns caused by elastic opening and closing of natural fractures in response to changing wellbore pressure during drilling

Wellbore ballooning occurs when natural microfractures open during circulation (mud gain) and close when pumps stop (mud loss), mimicking kick-loss cycles without an actual influx.

Which factor is the primary driver of 'bit whirl' in rotary drilling?

Answer: Lateral vibration caused by off-center rotation of the bit, leading to backward whirling and increased cutter wear

Bit whirl is a destructive lateral vibration mode where the bit center orbits backward around the wellbore rather than spinning in place, causing severe PDC cutter damage and poor ROP.

What is the 'wait and weight' method in well control, and how does it differ from the driller's method?

Answer: It circulates kill-weight mud from the bit to surface in a single continuous circulation, after first calculating and mixing the required kill mud weight

The wait and weight (engineer's) method mixes kill-weight mud before beginning circulation and circulates it in one pass, minimizing total annular pressure exposure compared to the driller's method.

How is 'pore pressure prediction' typically performed before drilling a new well?

Answer: By analyzing seismic velocity data, offset well logs, and basin modeling to estimate formation pressure before penetrating the zone

Pre-drill pore pressure prediction uses seismic interval velocities, regional geological knowledge, and nearby well data (d-exponent, sonic logs) to estimate abnormal pressures before drilling.

What is the purpose of 'centralizers' on casing strings during cementing?

Answer: To center the casing in the wellbore so cement can fill the annulus uniformly, preventing channeling and ensuring zonal isolation

Centralizers keep the casing centered in the borehole to ensure a uniform annular cement sheath around the pipe, which is critical for preventing mud channels that compromise cement integrity.