. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Figure 71-2. Tracts selected for sale. The environmental risks from both noise and physical disturbance can be minimized, if not elim- inated, by thoughtful planning and strict observance of sensible operating procedures. Environmental sensitivity, caution, and common sense are the main requirements for overcoming these environmental risks. The risks from normal operational discharges and accidental spills are more complex. Platform discharges Of the discharges t
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Figure 71-2. Tracts selected for sale. The environmental risks from both noise and physical disturbance can be minimized, if not elim- inated, by thoughtful planning and strict observance of sensible operating procedures. Environmental sensitivity, caution, and common sense are the main requirements for overcoming these environmental risks. The risks from normal operational discharges and accidental spills are more complex. Platform discharges Of the discharges to the environment resulting from oil and gas development, the discharge of mud and cuttings appears to be of most concern and will be the only one discussed in this chapter. Drilling fluids or "muds" perform a number of functions during the drilling process: they remove cuttings from the bore hole, cool and lubricate the TABLE Environmental risks and research opportunities 1301 drillstring and bit, form a filter cake on the wellbore which helps prevent losses in permeable formations, control high-pressure fluids in rock formations, suspend cuttings and heavy materials when circula- tion is interrupted, support part of the weight of the drillstring, control formation damage, facilitate well- logging, and transmit hydraulic power to the drill bit (McGlothlin and Krause 1980). All of these func- tions are essential to the completion of a well. The chemical additives commonly used in water-based drilling fluids sire barite, bentonite, lignite, and lignosulfonate (Perricone 1980). A wide variety of other materials are occasionally used, but these account for about 90 percent of the total tonnage of drilling-fluid additives. Barite is a mineral consisting primarily of barium sulfate. It is used to increase the density of drilling fluid in order to balance and control the pressures of the fluids in the rock formation being drilled. Up to 700 lb of barite may be used per barr
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