Drilling fluid

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Drilling fluid, also known as Drilling mud, is used primarily to keep a bore hole open & clean while earth drilling. The term fluids encompasses a broad range, including muds, water, and air.

[edit] Functions of Drilling Fluids

Primarily, the function of a drilling fluid is to:

Cool & clean the drill bit.
Provide up hole velocity for drill cuttings to get them out of the hole.
Keep the annular bore hole space clean to prevent friction & clogging.
Balance hydraulic pressures exerted by the earth on the bore hole.

[edit] Types of Drilling Fluid

^[1] Many types of drilling fluids are used on a day to day basis. Some wells require that different types be used at different parts in the hole, or that some types be used in combination with others. The various types of fluid generally fall into a few broad categories:

Air - compressed air is pumped either down the bore holes annular space or down the drill string itself.
Air/water - Same as above, with water added to increase viscosity, flush the hole, provide more cooling, and/or to control dust.
Air/polymer - A specially formulated chemical, most often referred to as a type of polymer, is added to the water & air mixture to create specific conditions. A foaming agent is a good example of a polymer.
Water - Water by itself is pumped down the bore hole or drill string.
Mud - Mud drilling is the use of water, or other medium, mixed with various clays, polymers, and/or other additives. Probably the most flexible type of drilling fluid.
Specialty drilling fluid - A synthetic fluid designed to do very specific things in very specific formations.