A fluid called mud circulates through the drilling bit as it cuts through rock. The fluid
lubricates the bit, removes rock cuttings, stabilizes the wall around the hole,
and controls the pressure in the wellbore. The mud is a suspension of chemicals
and minerals, such as bentonite clay in water or sometimes oil.
the mixture in the mud-mixing shack. The mud pumps push the fluid up the
standpipe and into the drill pipe through the kelly,
or through fittings in a top drive mechanism. After passing through
the drill bit, the mud and cuttings circulate back to the surface through the
space outside the pipe, known as the annulus, and into the return line.
shaker, a vibrating screen, then separates the cuttings from the mud. The
cuttings flow into lined pits or tanks, while the drilling mud flows through the
de-silter and is recirculated. More fluid is added through the mixer as the
drilling progresses to greater depths. When drilling is completed, the remaining
fluid is trucked away for disposal or reuse at another site.
Petroleum Communication Foundation. Our Petroleum Challenge: Exploring Canada's Oil and Gas Industry, Sixth Edition. Calgary: Petroleum Communication Foundation, 1999. With permission from the Centre for Energy.