Long-term effects of OBM cutting discharges in the sandy erosion area of the Dutch continental shelf

During drilling activities in the North Sea there has been an extensive use of oil based drilling muds (OBM) in the eighties and early nineties. With the discharges of drill cuttings substantial amounts of oil reached the seabed in those years. Research on the environmental impact of these discharges, based on the assessment of effects on the benthic fauna community, has been carried out on the Dutch Continental Shelf since 1985. From 1993 there is a complete ban on dumping of OBM-contaminated cuttings. However, research on the long-term effects of former discharges and, in particular, on the spatial extent of these effects was continued to assess possible recovery of sediment quality and benthic fauna. In 1993 a study was carried out at location P6b in the sandy erosion area in the southern part of the Dutch Continental Shelf. At platform P6b 4 wells had been drilled. The first well was drilled with OBM in 1985 and a first environmental survey was carried out in September 1985, 2 months after completion of the well. Later in 1985 and in 1986 2 more wells were drilled with water based muds (WBM) and the fourth well was drilled in 1987 using OBM again. This report presents the results of the 1993 survey, which took place 6 years after drilling of the last well. 15 figs., 13 tabs., 14 refs