API 13A Bentonite for Flush Drilling Fluid The most common use of bentonite is in drilling fluids. The bentonite in the flush fluid lubricates and cools the cutting tools while protecting against corrosion. As the drilling fluid generates hydrostatic pressure in the borehole, it hinders fluid and gas penetration. stic Viscosity Ratio Residue of diameter greater than 75 Moisture content (%) Â 12.max pH Â 8 - 10.5
