bentonite — Oil & Gas Glossary
A claymineral that is composed principally of three-layer clays, such as montmorillonite, and widely used as a mud additive for viscosity and filtration control. Commercial bentonite ores vary widely in amount and quality of the swelling clay, sodium montmorillonite. Ores of lower quality, those with more calcium-type montmorillonite, are treated during grinding by adding one or more of the following:
Detailed Explanation
sodium carbonate, long-chain synthetic polymers, carboxymethylcellulose (CMC), starch or polyphosphates. These help make the final product meet quality specifications. Unfortunately, the additives may not remain effective in "the real mud world" when in use at the rig due to hardness ions in the water, high temperature, bacterial attack, mechanical shear-degradation and other factors that can render these additives ineffective.