Seafloor Monitoring for Synthetic-Based Mud Discharged in the Western Gulf of Mexico

Abstract

Abstract Synthetic-based muds have been used to simultaneously improve drilling and environmental performance. The fate and effects of synthetic-based mud discharges in the marine environment have been issues of concern with the drilling industry and governmental agencies. Most of the environmental data on synthetic-based muds have been generated under laboratory conditions. This study uses field-collected data to investigate the fate and effects of a polyalphaolefin synthetic-based drilling fluid. The first well drilled in the Gulf of Mexico using synthetic-based mud was completed in June 1992. Approximately 441 bbl of cuttings and 354 bbl of synthetic-based mud were discharged over a 9-day period. Three sampling trips have been made to the discharge location to collect sediment samples for chemical and biological analysis over a 2-year period. The sediment samples were analyzed for content of organic compounds and barium. On the third trip, infaunal samples were also taken. Information collected from the chemical and biological analysis is documented and compared to similar field studies performed on oil-based and water-based muds. Sampling techniques and analytical protocols are described to facilitate future studies. Two years after discharges of synthetic-based cuttings were completed, an area within 50 m of the discharge point continued to exhibit alterations in the benthic community not normally associated with water-based mud discharges. However, the study indicates that polyalphaolefln synthetic-based mud exhibits significant improvements over oil-based mud in terms of removal of organic contamination and minimization of adverse effects on the benthic community. Introduction The discharge of drilling muds and drilled cuttings into aquatic environments is a growing issue of environmental concern worldwide. Regulations allow water-based muds (WBMs) that meet permit limitations to be discharged in OCS waters of the USA. Oil-based muds (OBMs) and cuttings discharges have been prohibited in the Gulf of Mexico for some time. However, discharge of OBMs has continued to be permitted in the North Sea under increasingly strict regulations. As part of the regulatory process, North Sea operators have been required to perform detailed chemical and biological site assessments of locations that use OBM. In 1985, the Paris Commission Working Group on Oil Pollution considered the environmental data available and compiled a list of "agreed facts" which described the scale of contamination from OBM, and the extent of the biological effects of OBM discharges. The main points of the "agreed facts" are summarized below. P. 51