Environmental effects of a discharge of drill cuttings contaminated with ester-based drilling muds in the North Sea

Abstract

From the Abstract: “A field-monitoring program has been carried out to assess the environmental effects associated with drill cutting discharges at a drilling location in the North Sea, after drilling with ester-based muds. The study included a baseline survey just before drilling started and three postdrilling surveys, 1, 4, and 11 months after termination of drilling. During these surveys, ester concentrations and macrofauna densities were determined at distances between 75 and 3,000 m from the well. For the first and second postdrilling surveys, ester concentrations ranged between 2 and 4,700 mg·kg−1 dry sediment. During the third survey, esters were detected up to 200 m, with concentrations between 1 and 250 mg·kg−1 dry sediment. Between 500 and 3,000 m, ester concentrations were below detection level. The half-life was estimated as 133 d. This value reflects the composite effects of biodegradation and sediment relocation. During the second postdrilling survey, a reduced abundance as well as a reduced species richness of the macrofauna was observed up to 200 m from the well. Also, the presence of Capitella capitata was an obvious sign of disturbed sediment conditions in this area. A few species showed abundance gradients over the whole sampling transect and occurred in reduced abundance up to 500 or 1,000 m compared to the 3,000-m reference station. The third postdrilling survey clearly revealed effects at 75 to 200 m from the well. At distances ≥500 m, persistent effects could no longer be demonstrated. Although the results of the present study show that effects had not completely disappeared after 1 year, there are signs of recovery of the macrobenthos, because a reasonable number of species had recolonized the area in the vicinity of the well site, particularly at 200 m, in fairly high numbers.”