Overview of Drill Cuttings Management Options Through Modeling, Monitoring and Life Cycle Assessment

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Abstract Drilling operations produces drill cuttings, which need to be managed to minimize their potential environmental impacts. Nowadays, legislation worldwide moves towards limiting discharge at sea to decrease impacts on ocean. But cuttings must still be managed, and alternatives are not necessarily more environment friendly. In this article, three approaches of cutting management environmental impacts were compared. Modeling studies were compared to field data, to assess the relevance of these modeling studies in the evaluation of drilling discharge acceptability. The results of monitoring campaigns conducted on three offshore field in Myanmar, Congo and Angola were collected and analyzed. Lastly, a comparative attributional life cycle analysis (or LCA) of drill cuttings management options was conducted, comparing discharge at sea, reinjection into a disposal well, onshore landfill containment and onshore thermo-desorption. Environmental risk calculation through discharge modeling is robust and constitutes a good tool to evaluate the drilling discharge strategy, but it focuses on the sole discharge at sea option. Results from monitoring campaigns shows that fifteen to twenty years after drilling operations, decreasing trends are observed for drill cutting tracers. For other metals, concentration levels are similar to those of the baseline. Slight impacts on benthic macrofauna community keep on being observed, and processes of initial diversity recovery are in progress locally. At the scale of the entire fields, biodiversity has recovered almost similar levels as initially. With current practices, impacts can be estimated to last around ten years. The LCA was hampered by a lack of standardized indicators for marine compartment impacts and poor characterization of some drilling muds additives in LCA reference databases. Considering these limitations, the results and their interpretations state a higher impact of onshore management with thermo-desorption on most indicators. Discharge at sea has the biggest initial impact on marine ecotoxicity. Onshore landfill has the biggest impact on freshwater eutrophication, freshwater ecotoxicity, human carcinogenic toxicity and land use. This study shows that given current practices, impacts of drill cuttings discharge at sea are well predicted and last around 10 years. Alternative management options have impacts as well, mainly on human health, land use and non-marine environmental compartments. Decision-makers must balance the impacts on each compartment to choose the better management option given the context they face. This study highlights the interest of using life cycle analyses to compare management options rather than focusing on the impacts of only one option. To be able to do so, there is a need of developing LCA methodology on marine compartments.