1. n. [Drilling Fluids]
A finely divided, solid material dispersed in a liquid medium. The solid particles scatter a light beam and do not settle by gravity; they are usually less than 2 microns in diameter. Some drilling fluid materials such as bentonite clay, starch particles and many polymers become colloidal when used in a mud. Oil muds contain colloidal emulsion droplets, organophilic clays and fatty-acid soap micelles.