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API 4397

1985 Edition, June 1, 1985

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Chronic Effects of Drilling Fluids Discharged to the Marine Environment

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Product Details:

  • Revision: 1985 Edition, June 1, 1985
  • Published Date: June 1985
  • Status: Not Active, See comments below
  • Document Language: English
  • Published By: American Petroleum Institute (API)
  • Page Count: 171
  • ANSI Approved: No
  • DoD Adopted: No

Description / Abstract:

The first offshore oil well was drilled from a wooden pier extending into the surf zone near Summerland, California in 1896. By the end of 1982, approximately 27,000 wells had been drilled in U.S. coastal and outer continental waters (API, 1982). It is expected that by 1985, 1,485 wells per year will be completed off the U.S. coast. The U.S. Geological Survey has estimated that as much as 33.8 percent of the nation's undiscovered recoverable oil and 28.1 percent of undiscovered natural gas may lie beneath U.S. coastal and outer continental shelf waters (Kash, 1983).

During the drilling of exploration and production wells, a variety of liquid, solid and gaseous wastes are produced on the drilling rig or platform. Some of these wastes are discharged to the ocean. Such discharges are regulated by the Environmental Protection Agency through issuance of National Pollutant Discharge Elimination System (NPDES) permits. A permit is issued if EPA determines that the discharge will not cause "unreasonable degradation" of or "irreparable harm" to the receiving waters (Beller, 1983). If EPA is uncertain about the environmental impact of a discharge, it may impose mitigative measures or require monitoring or bioassay programs as conditions for issuance of a permit.

Liquid and solid wastes that may be permitted for discharge to the ocean include cooling water from machinery, deck drainage following treatment in an oil/ water separator, domestic sewage following primary treatment and chlorine addition, drill cuttings and water-base drilling fluids. Of the permitted discharges, those of drilling fluids and drill cuttings are quantitatively the most important and have generated the greatest concern about possible adverse environmental impacts of offshore exploration and development. The environmental concerns relating to ocean discharge of used drilling fluids are that they may be acutely toxic or produce deleterious sublethal responses in sensitive marine species, they may alter the physical characteristics of benthic habitats by accumulating on the bottom, and potentially toxic chemicals sometimes associated with drilling fluids may be accumulated by marine organisms to concentrations that would be harmful to the organisms themselves or to consumers, including man (Richards, 1979; Rieser and Spiller, 1981).

Recently, these concerns were evaluated in depth by the Panel on Assessment of Fates and Effects of Drilling Fluids and Cuttings in the Marine Environment, under direction of the National Research Councilof the National Academy of Science (NAS, 1983). The panel concluded that more than 90 percent ofused water-base drilling fluids tested to date wereonly slightlytoxic or practically non-toxic (96 hr, median lethal concentration greater than 1,000 mg/ liter) to a wide variety of marineorganisms, Chronicand sublethal responses in sensitive life stages and species may be observed at concentrations one to two orders of magnitude lower than acutely lethal concentrations, but still much higher than concentrations expected in the water column near the discharge site. Because of rapid dilution and dispersion of drilling fluids in the water column, little or no adverse impacts of drilling fluid discharges are expected to water-column organisms. However, heavier fractions of drilling fluid solids may accumulate on the bottomnear the discharge site and cause localized adverse impacts on benthic and demersal organisms.

The NAS (1983) report goes on to state that many of the experimental designs of sublethal and chronic effects studies haverelied on exposure regimes that do not simulate the rapid dispersion and fractionation of drilling fluids in the water columnand their movements along and mixing with the bottom sediments. The report recommends that: "any additional research on drilling fluids should include acute, sublethal and chronic bioassays wing techniques and contaminant exposures that reflect actual discharge and exposure conditlons---".