Assessment of Environmental Impacts from Drilling Muds and Cuttings Disposal, Offshore Brunei

摘要

In 2000-2001, an offshore survey and environmentalrnassessment were conducted of drilling activities offshorernBrunei (Adinin-Jacques Whitford1). A primary focus was tornevaluate the environmental effects of disposal of oil basedrnmud (OBM), ester-based synthetic mud (ESBM), and waterrnbased mud (WBM) in the tropical marine environment of thernSouth China Sea.rnA number of well sites were surveyed for each of the mudrntypes, encompassing varying water depths (20 - 500 m) andrntime elapsed since drilling. Key parameters (e.g.,rnhydrocarbons, esters, metals and redox) were examined at allrnsampling locations, depending on the drilling muds used.rnSide-scan sonar, detailed hydrographic imaging, sea bedrnvideo, current information, and benthic sampling results werernalso interpreted. A modified radial sampling pattern was used.rnThe study concluded that the magnitude and persistence ofrnenvironmental effects from discharge of drilling muds andrncuttings range, in order of severity, from OBM to ESBM tornWBM. The study found that OBM and cuttings are toxic tornmarine life and can persist on the Brunei sea bed for over 13rnyears. Biophysical effects on the sea bed from both WBM andrnESBM are similar, and result primarily from smothering ofrnbenthic organisms by sedimentation and anoxic conditions duernto bacterial decomposition within the cuttings piles. WBMrneffects were, however, noted to be more widely dispersed (>rn1200 m) and exhibited indications of faster benthos recoveryrn(within 3 years) than ESBM (typically dispersed withinrn200 m).rnThe survey results and detailed habitat sensitivity mappingrnwere used to prepare comprehensive site-specific guidelinesrnfor WBM and ESBM disposal offshore Brunei. Using arn“receiving environment” approach, the guidelines specifyrndetailed instructions for WBM and ESBM offshore disposal inrneach of seven management areas ranked according tornenvironmental sensitivity.