Drilling Track: Rigs, Well Control and Geothermal · Module 2 of 4 · about 15 min
Mud and well control
Drilling fluid, called mud, does several jobs at once. It carries cuttings up out of the hole, cools and lubricates the bit, holds the hole walls up and, most important, puts pressure on the formation to keep oil, gas or water from flowing in.
That pressure is hydrostatic: the weight of the fluid column. In oilfield units it is pressure in psi = 0.052 × mud weight in pounds per gallon × true vertical depth in feet. For example, 10 ppg mud at 10,000 feet gives about 5,200 psi. If formation pressure is higher than that, fluid comes in.
An unplanned influx is called a kick. Warning signs include a gain in the mud pits, flow from the well with the pumps off, a jump in return flow and a sudden faster drilling rate (a drilling break). When a driller sees signs, the standard move is to check for flow and, if the well is flowing, shut it in with the BOP. An uncontrolled kick is a blowout.
Pulling pipe out of the hole lowers the mud level and can swab fluid in, so the crew fills the hole and tracks how much mud it takes on every trip. A trip sheet that does not add up is a warning sign.
Sources
Module quiz
5 questions, 4 correct to pass. You'll see what you missed and why, and you can retake it.