Quantitative Assessment Of The Environmental Impact Of Offshore Drilling Activities Using Benthic Fauna: Lessons Learnt From Actual Cases

Since the onset of offshore drilling, the drilled cuttings and their disposal have received much attention in the oil and gas industry. Numerous studies performed in the laboratory on the foreseeable fate of cuttings have led to the research for new formulations with the objective of achieving lower toxicity and better intrinsic biodegradability. The study of the marine environmental impact associated with the discharge of drilled cuttings has already given rise to numerous works and surveys related to the North Sea, but it is clear that knowledge is still limited. Further information is required on the monitoring of sediments contaminated with cuttings, especially in warm sea conditions. On this topic, research projects were conducted between 2000 and 2006 in West Africa (Congo, Gabon and Angola) in order to study the modes of regeneration of the benthic fauna and the recolonisation of the seabed after the discharge of cuttings. In addition to classical approaches concerning systematic study of the abundance and diversity of the macrobenthos (> 1 mm), physicochemical analyses on sediment, biodegradability and lixiviation, new methodologies based on toxicological tests and the study of foraminifers were applied. We show that these methodologies are adapted to extreme conditions such as deep and ultra deep environments and enable different sites to be compared at large scale conferring ubiquity of the methods. In a more general context of the environmental constraints of oil industry, our work demonstrated the geographically limited extent of the impacted zones, the absence of significant long-term modification of the adjacent ecosystems and the possible application to other discharge sites