RIASSUNTO
Abstract
In 2000-2001, an offshore survey and environmental assessment were conducted of drilling activities offshore Brunei (Adinin-Jacques Whitford1). A primary focus was to evaluate the environmental effects of disposal of oil based mud (OBM), ester-based synthetic mud (ESBM), and water based mud (WBM) in the tropical marine environment of the South China Sea.
A number of well sites were surveyed for each of the mud types, encompassing varying water depths (20 - 500 m) and time elapsed since drilling. Key parameters (e.g., hydrocarbons, esters, metals and redox) were examined at all sampling locations, depending on the drilling muds used. Side-scan sonar, detailed hydrographic imaging, sea bed video, current information, and benthic sampling results were also interpreted. A modified radial sampling pattern was used.
The study concluded that the magnitude and persistence of environmental effects from discharge of drilling muds and cuttings range, in order of severity, from OBM to ESBM to WBM. The study found that OBM and cuttings are toxic to marine life and can persist on the Brunei sea bed for over 13 years. Biophysical effects on the sea bed from both WBM and ESBM are similar, and result primarily from smothering of benthic organisms by sedimentation and anoxic conditions due to bacterial decomposition within the cuttings piles. WBM effects were, however, noted to be more widely dispersed (> 1200 m) and exhibited indications of faster benthos recovery (within 3 years) than ESBM (typically dispersed within 200 m).
The survey results and detailed habitat sensitivity mapping were used to prepare comprehensive site-specific guidelines for WBM and ESBM disposal offshore Brunei. Using a ""receiving environment"" approach, the guidelines specify detailed instructions for WBM and ESBM offshore disposal in each of seven management areas ranked according to environmental sensitivity.
Introduction
Brunei Shell Petroleum (BSP) has undertaken exploration drilling and production of oil and gas in the offshore waters of Brunei since 1951. During this period, hundreds of exploration wells were drilled, mostly in the coastal area of the offshore concession (less than 70 m water depth). An extensive array of pipelines, well jackets, and production platforms has also been installed to recover oil and natural gas reserves.