Deposition of drilling particulates off Point Conception, California

Abstract

From the Abstract: “Three offshore oil production platforms discharged over 40000 m3 of drilling fluid during a period of biological and chemical sampling which was conducted on the continental shelf adjacent to Point Conception during 1987 and 1988. Sediment-trap arrays were deployed at distances ranging between 0.5 and 6.5 km from the northernmost platform and the depositional flux of drilling-derived particulates was estimated from elevated barium concentrations in trapped sediments. The maximum flux of drilling solids, near 500 mg m-2 day-1, represented less than 2% of the total particulate flux into the sediment traps. Particle trajectory computations; based on direct current measurements, the time history of drilling-fluid discharges from the platforms and drilling-floc settling speed indicate that ambient current flow carried discharges over significant distances toward the northwest. The resulting seafloor depositional pattern compares favorably with the observed temporal and spatial pattern determined from the sediment traps. The results indicate that a substantial portion of the trapped drilling solids originated from the two distant platforms located 3.5 and 6.8 km to the south-east and cessation of drilling on these platforms accounts for the observed temporal decline in drilling particulates trapped near the northernmost platform where the discharge was continuous.”