What causes differential sticking?

• A. Differential sticking occurs when a drill pipe gets stuck against the walls of the borehole.
• B. Differential sticking is caused by mud loss.
• C. It is caused by formation gas influx.
• D. It is caused by casing failure.

Answer: (A)

Differential sticking arises when the drill string is pressed against the borehole wall because of a pressure difference between the formation pore pressure and the hydrostatic pressure of the drilling mud. If the formation pressure exceeds the mud pressure, the outside force on the pipe pushes it toward and against the wall. With the pipe contacting the wall, the mud cake and restricted annular clearance create substantial friction, making it difficult or impossible to move the string even with surface torque. This combination of external pressure and friction causes the pipe to become stuck. It’s not caused by mud loss, gas influx, or casing failure, which are different drilling issues.