Environmental aspects of drilling fluid and drill cuttings disposal

More than 21,000 wells have been drilled for hydrocarbons in the offshore United States since 1947, with no known permanent damage to the marine biota from the discharged drilling mud and cuttings. However, public awareness of environmental aspects which has increased so dramatically in the last decade has brought considerable attention to bear on the possibility that perhaps muds and cuttings might have some deleterious effect on the marine environment. Several million dollars have been spent by the oil industry on laboratory and at-sea studies to determine exactly what environmental impact would result from drilling a well in a given area and in discharging into the water the drilling mud and cuttings. At the present time there exists more than 150 North American publications and reports dealing with volumes of mud and cuttings discharged from offshore wells; dilution, dispersion, settling and final disposition of mud and cuttings; toxicity and bioassay studies of whole mud and mud components; acceptable procedures for such studies; and closely related topics that have some direct bearing on the effect of these discharges. There are at least ten times that many additional pertinent papers of interest which cover such topics as trace metals and other chemical constituents of oceanic waters and sediments, sedimentation rates, currents, distribution and concentrations of various marine organisms, and which allow comparisons with impact from sewage disposal, dredging activities and effects of trawling and other fisheries activities. Presumably there are a number of reports and publications from other countries having to do with offshore oil and gas drilling activities in other seas. Additional studies concerned with well discharges are currently either underway or in the planning stage in the Gulf of Alaska, Gulf of Mexico, and offshore California and several Atlantic states. The conclusion that must be reached after , studying a large number of these reports and publ- - ications is that, except in rare and unusual circumstances, the discharge of drilling mud and cuttings from normal well drilling operations has not caused and will not cause serious environmental damage. There is no question that drilling mud, mud components and cuttings are acutely toxic (i.e. can cause death) to various organisms if the concentrations are great enough, as is adequately shown by the results from the vast number of static bioassays that have been conducted. There is also no question that dilution and dispersion lower concentrations such that the discharge will cause neither immediate nor long-term damage. Some of the studies and their results are discussed in this paper, and an abbreviated bibliography is included for reference.