Linked from
The 9 pages that link to Drilling fluid, each with the reason it gives.
Clay mineralRelated: Bentonite suspensions provide viscosity and help stabilize boreholes.
BoreholeRelated: Its properties help control the borehole during drilling.
BaryteRelated: Ground baryte raises drilling-fluid density to help control formation pressure.
HectoriteRelated: Hectorite can serve as a rheology modifier in specialized drilling fluids.