Impact of Drilling Activities in Warm Sea: Recolonization Capacities of Seabed

Abstract

Due to large constraints in environmental regulations, discharge of drill cuttings at sea has to be controlled. It is therefore necessary to get basic information in order to select environment-friendly drilling fluids. The present study was intended to assess the impact of cuttings, the capacity of regeneration of the ecosystem and the processes of recolonization of seabeds. In a first phase, standardized (OSPAR) and experimental toxicity tests, aerobic and anaerobic degradation measurements and lixiviation tests were performed on various types of muds and cuttings (containing diesel oil, two different paraffinic oils, and glycol) in laboratory conditions. In a second phase, the most suitable measurements were taken within the framework of an in situ experiment at a discharge site in Congo (Africa). Cuttings discharge began in November 1993 and ended in April 1999. Together with this survey, a complete analysis of benthos was performed eight years after the beginning of cuttings discharge. The preliminary results demonstrated: - the zone of extension of the toxicity inducing benthos modifications was less than a few hundred meters around the discharge site; - original fauna was replaced by a more specific fauna. In the more general context of the environmental constraints in the oil industry, our work demonstrated the containment of the impacted zones, the absence of significant risks of modification of the adjacent ecosystems and the possible application to other discharge sites.