Drilling mud. A drilling mixture consisting of one or two liquid phases and dissolved and undissolved solids with properties tailored to a particular problem. It cools and lubricates the drilling bit, conditions the formation wall. removes cut tings from the borehole, brings traces of formation fluids to the surface, and, when it possesses certain characteristics, it provides a wellbore medium suitable for some electrical, acoustic, and nuclear well-logging measurements. See also oil emulsion, invert oil emulsion, oil-base mud, and water-base mud.