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

摘要

Drilling operations produces drill cuttings,which need to be managed to minimize their potentialenvironmental impacts.Nowadays,legislation worldwide moves towards limiting discharge at sea todecrease impacts on ocean.But cuttings must still be managed,and alternatives are not necessarily moreenvironment friendly.In this article,three approaches of cutting management environmental impacts were compared.Modelingstudies were compared to field data,to assess the relevance of these modeling studies in the evaluationof drilling discharge acceptability.The results of monitoring campaigns conducted on three offshore fieldin Myanmar,Congo and Angola were collected and analyzed.Lastly,a comparative attributional lifecycle 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 toevaluate the drilling discharge strategy,but it focuses on the sole discharge at sea option.Results frommonitoring campaigns shows that fifteen to twenty years after drilling operations,decreasing trends areobserved 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 diversityrecovery are in progress locally.At the scale of the entire fields,biodiversity has recovered almost similarlevels as initially.With current practices,impacts can be estimated to last around ten years.The LCA washampered by a lack of standardized indicators for marine compartment impacts and poor characterization ofsome drilling muds additives in LCA reference databases.Considering these limitations,the results and theirinterpretations 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 impacton 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 predictedand 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 eachcompartment 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 ratherthan focusing on the impacts of only one option.To be able to do so,there is a need of developing LCAmethodology on marine compartments.