Properties and Treatment of Rotary Mud

The subject of mud sounds so simple, uninteresting and unimportant that ithas failed to receive the attention that it deserves, at least as applied tothe drilling of oil wells. As a matter of fact, it is one of the mostcomplicated, technical, important and interesting subjects in connection withrotary drilling. In 1923, R. E. Collom said "It should be possible toestablish certain physical standards for mud fluid, " but while considerablework has probably been done on the subject before and since that time, andnumerous articles have been written, the progress of general knowledge of thesubject and the application of better practices have not kept pace with otherdevelopments in rotary drilling, and physical standards cannot be considered asestablished. Mud is apt to be thought of as an accessible and cheap material, but itscost is likely to be an important factor in the total cost of drilling a well. Some wells "make" most of their own mud out of the formations drilled, but in most cases a great deal of mud-making material has to be supplied frommore or less distant sources. Expenditures for mud materials by one Californiacompany totaled practically one-quarter million dollars during 1929 andaveraged about 13 per rig per drilling day, or about 2000 per well. Underunfavorable conditions, mud cost may reach many times this figure. Parker2 saysthat in the Hobbs, N. M. , field "as much as 75, 000 has been spent on onewell alone for mud and mud-weighting compounds. " Presumably this is anexceptional case. Unit cost of mud fluid will range from 10 c. per barrel, where suitable material is close at hand, to 1 where crude material isavailable at moderate price but must be hauled long distances, and on up to asmuch as 11 per barrel where high gas pressure requires the use of specialprocessed weighting material. The cost of mud pales into insignificance, however, when the results ofusing improper mud are considered. Blow-outs and lost circulation are obviouslythe result of inadequate mud. Stuck drill pipe, whether or not twisted off, inmany if not most cases probably is caused by cuttings settling out of the mudor the mud itself precipitating.