Drilling fluid

Drilling fluid is a liquid or gas circulated through a borehole during drilling. It carries rock cuttings to the surface, cools and lubricates the drill bit, and helps control formation pressure.

Drilling mud: A liquid-based drilling fluid formulated with solids and chemicals to perform drilling functions. This common drilling-fluid form uses engineered density and rheology to lift cuttings and resist formation pressure.
Bentonite: A clay-rich material dominated by montmorillonite that swells when exposed to water. Its swelling particles help build viscosity and form a low-permeability filter cake.
Water-based mud: Drilling mud whose continuous liquid phase is water or brine. It is widely used where water compatibility and cost suit the formation and well design.
Air drilling: A drilling method that uses compressed air or gas instead of liquid drilling fluid to remove cuttings. It avoids liquid mud in suitable formations but cannot provide the same hydrostatic pressure support.
Deepwater Horizon oil spill: The 2010 blowout and oil spill from the Macondo well in the Gulf of Mexico. The disaster exposed how failure to maintain well barriers can overwhelm drilling-fluid pressure control.
Mud weight: The density of drilling fluid, commonly expressed in pounds per gallon or kilograms per cubic meter. Its hydrostatic pressure helps balance pressure in permeable formations.
Barite: A dense barium sulfate mineral used as a weighting material in drilling fluids. Adding barite raises fluid density without requiring an excessively high solids volume.
Oil-based mud: Drilling mud whose continuous liquid phase is oil or synthetic fluid. Its temperature stability and shale inhibition suit difficult formations, though disposal is more demanding.
Foam drilling: A drilling method that uses gas-liquid foam to transport cuttings through a borehole. Foam occupies a middle ground between dry gas circulation and conventional liquid mud.
Macondo well: The deepwater exploration well whose 2010 blowout caused the Deepwater Horizon disaster. Its cementing and well-control failures made drilling-fluid operations central to later investigations.

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