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Offshore Drilling Discharges
Drilling oil and gas wells requires the use of drilling fluids to remove rock "cuttings" from the wellbore and to control formation pressure. Drilling fluids are made of various chemical compositions depending on the geologic and reservoir formations being drilled. These fluids are pumped down the hole and transported back to the surface with the cuttings that are "cut loose" as we drill. The cuttings are then separated from the drilling fluid at the surface. In the offshore environment, depending on the chemical composition used and local conditions, cuttings with residual drilling fluids are often discharged to the sea. This discharge must be carefully managed to minimize its impact on the marine environment.
In reviewing our worldwide offshore drilling fluid management practices in 2002, we identified several opportunities for improvement. As a result, ChevronTexaco is developing a new performance standard that uses ecological risk criteria to define what can and cannot be discharged into water and establishes buffer zones to help protect biologically sensitive areas. It also requires new offshore drilling projects to evaluate the technical and economic feasibility of reinjecting cuttings back into subsurface formations, instead of discharging them into the sea.
Under the standard, all offshore drilling rigs using drilling fluids that are not water-based will be equipped with advanced cuttings cleaning systems. Such systems reduce the environmental impact of discharging drilled cuttings to the sea.
The standard also requires all drilling projects to undergo a risk-based screening to determine the adequacy of environmental practices. The screening considers site-specific factors such as ocean depth and prevailing currents, toxicity and biodegradation of drilling fluids and the volume of cuttings generated. This information is used to determine whether discharging is acceptable in a given location and to identify the appropriate cleaning technology to help protect the local marine environment.
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