Water-based drilling mud most commonly consists of bentoniteclay (gel) with additives such as barium sulfate (barite), calcium carbonate (chalk) or hematite. Various thickenersare used to influence the viscosity of the fluid, e.g. xanthan gum, guar gum, glycol, carboxymethylcellulose, polyanionic cellulose (PAC), or starch. In turn, deflocculants are used to reduce viscosity of clay-based muds; anionic polyelectrolytes (e.g. acrylates, polyphosphates, lignosulfonates(Lig) or tannic acidderivates such as Quebracho) are frequently used. Red mud was the name for a Quebracho-based mixture, named after the color of the red tannic acid salts; it was commonly used in 1940s to 1950s, then was made obsolete when lignosulfonates became available. Other components are added to provide various specific functional characteristics.
Barium sulfate (BaSO4)
About 80% of the world's barium sulfate production, mostly purified mineral, is consumed as a component of oil well drilling fluid. It increases the density of the fluid.
Sodium silicate (Na2SiO3)
Sodium silicate, also known as water glass , is frequently used in drilling fluids to stabilize borehole wells and to avoid the collapse of bore walls. It is particularly useful when drill holes pass through argillaceous formationscontaining swelling clay minerals such as smectiteor montmorillonite.
