Drilling mud—also called drilling fluid—is an essential component of the drilling process. Drilling mud aids in the process of drilling a borehole into the earth. Such holes are drilled for oil and gas extraction, core sampling and a variety of other purposes.
The fluid is used to lubricate the drill bit and transport the drill cuttings to the surface (U.S. Environmental Protection Agency, www.epa.gov). Drill cuttings are broken bits of solid material that are produced as the drill bit breaks the rock. As it circulates up from the drill bit, the drilling mud carries drill cuttings up to the surface, where the mud and the cuttings are separated.