ABSTRACT
When a hole is drilled into the earth, the earth material removed as the hole progresses, is scraped, chiseled, and hammered out-of-place. Mechanical work is done on the rock material in the vicinity of the borehole. The borehole is filled with a drilling fluid which is continuously pumped into the hole from the surface, at near-surface temperature. It may not, at all, resemble the native fluids. This fluid is pumped down the drill pipe and up the annulus. The function of the drilling mud is to cool and lubricate the drill bit, carry cuttings out of the hole, and to counter the hydrostatic head of the formation. Occasionally brine is used in or as a mud. This is done when the formation clays are prone to swell; when they are partially desiccated. The examination and logging of the solid cuttings of the formation rock brought to the surface by the mud are usually done by the project geologist.
