Aged Drilled Cuttings Offshore Gabon: New Methodology For Assessing Their Impact

During E&P offshore activities, and in particular during drilling operations, the living conditions of the flora and fauna on the seabed may be disturbed. The paper describes the study made for assessing the actual impact of the discharged cuttings, the regenerating capacity of the ecosystem and the medium and long-term recolonization processes, based on in situ measurements. A previous study undertaken on cuttings recently discharged offshore Congo measured kinetics of space and time restoration of the drilling site. To validate the results we carried out a similar study dedicated on aged cuttings offshore Gabon. Usual process for monitoring biological effects of cuttings includes several approaches such as benthic macrofauna (> 1mm size) studies, physicochemical analysis of sediment and ecotoxicological tests. One of the key features of our study was to add, to this process, a study of the benthic meiofauna (0.1 to 1mm size). Experiments conducted demonstrated: • very low concentrations of hydrocarbons stemming out from the cuttings, • a very low toxicity of sediment, • no benthic macrofauna community alteration, • no change in the communities of actual and fossil foraminifera (meiofauna) and, • last but not least, that the study of the benthic meiofauna improves the quality of the assessment made. Introduction In order to study the way the benthic fauna regenerates and recolonises the seabed after the discharge of cuttings in a warm water context, a project was conducted in 2 phases between 2003 and 2004 off Congo with different objectives: • To validate an experimental protocol for monitoring recolonization of aged cuttings. We focused on the impact of oily cuttings, • To assess the impact of cuttings contaminated by oil based drilling fluids and the capacity of regeneration of the environment over time. [1-5] Off Congo, the last survey was realized 4 years after the end of cuttings discharge. To validate the Congo results, we carried out a similar study but on aged dumped oil based cuttings (12 years after cessation of the disposal activities) offshore Gabon.