Drilling Fluid Selection Methodology for Environmentally Sensitive Areas

Abstract

Abstract When operating in areas of Africa which are particularly sensitive environmentally selection of drilling fluids should take into account both technical and environmental criteria in regards to the treatment and disposal of the cuttings and excess fluids. In this particular case the operator's choice of drilling fluid during its exploration and appraisal campaign was driven primarily by the need to use fluids with green credentials, and the fact that the exploration wells were not particularly demanding from a technical point of view. However, it was recognised that a system with improved technical performance woud be required when drilling the anticipated, more demanding, high angle and extended reach wells during the development drilling. When enough core and drill cuttings became available a thorough study was performed which comprised shale characterisation and inhibition testing. Seven drilling fluid compositions were tested, six water based and one synthetic based. A simple rating method was devised for ranking technical and environmental performance as well as treatment and disposal options for each fluid. The synthetic based mud was the strongest technically followed by an amine-modified high-performance water based system. It was shown that both can be combined with techno-economically feasible treatment and disposal options that minimise environmental impact.