Environmental impact of oil-based mud cuttings  discharges--a North Sea perspective

Abstract

Discharges of Oil-Based Mud Cuttings have an environmental impact which is limited in time and in volume/area. North Sea field data (1979–1982) indicates that beyond the immediate neighbourhood of the discharge, the hydrocarbon concentrations in the water column are effectively at ambient levels and environmental impact, if any, is difficult to establish. Regarding the sea-bottom ecology the data shows the existence of three different zones: a) A proximal zone, extending about 300–700 m from the platform, where cuttings form a surface deposit (thickest at the source and quickly thinning outward). Anaerobic conditions exist with associated hydrogen sulfide and bio-degradation will be slow. Environmental impact will be most significant in the immediate neighbourhood of the source; any recovery will be slow. B) A distal zone, reaching beyond the proximal zone out to roughly 1500–5000 m, where cuttings may be found as think patchy deposits of tiny particles, where aerobic conditions exist, and where biodegradation can readily take place. Environmental impact, if any, will be light, and recovery quick. c) The far zone, beyond some 1500–5000 m, where no environmental impact can be identified. Local circumstances will determine the actual condition around each source.