Water as a drilling fluid does not qualify as a mud. If there are no hole (formation) problems that prevent its being the most economical drilling fluid; if neither the geologist, palentologist, nor production supervisor have valid objections; and if it is available, water is seldom if ever surpassed. When the formation requires, or a supervisor demands , filtrate control and / or viscosity and /or gels in the drilling fluid, a “mud” is built. Or if the fluid density required is too high for salt water alone , mud properties are required to suspend barites.
The overall efficiency of cuttings removal by the solids-control system, Es, can be expressed as:
Es = E1 f 1 +( 1 – E1 )E2 f 2 + ( 1 – E2 )E3 f 3 +( 1 – E3 )E4 f 4 (1)