Environmental Impact Assessment of Current Synthetic Drilling Fluids in Offshore Oil Fields Using Modified CO2 Evolution Respirometry Technique

Abstract

AbstractSynthetic fluid biodegradation test is one of the essential requirements by environmental regulatory agencies before an approval for offshore cuttings disposal can be granted.In this study, the aerobic biodegradation tendencies of two industry grade, deep-water synthetic hydrocarbon-based fluids (SHBF and SEBF) were investigated using modified carbon-IV-oxide (CO2) evolution respirometry technique. The results were compared with an ester synthetic fluid that was code-named as ternary mixture of synthetic ethyl esters of plants oil (SEEP-Mixture). A known concentration of the test drilling fluids and reference chemicals was inoculated in a mineral medium, pre-conditioned and incubated by the passage of CO2 free air under aerobic condition in the dark for a period of twenty-eight (28) days at the test temperature of 58°C± 2°C in an aerobic digester. The amount of CO2 evolved from the exhaust air of each composting vessel at intermediate time intervals was measured as dissolved inorganic carbon (DIC) by absorption in Ba (OH)2 solution using titration technique. Sodium benzoate (C6H5COONa) was used as reference fluid sample. The tests were conducted under OECD and OSPAR Commission recommended standard protocols for testing chemicals in the offshore oil industry.The SEEP mixture ester fluid and the sodium benzoate reference fluid sample are inherently and readily biodegradable because more than 60% of their theoretically available carbon IV Oxide (ThCO2) have been converted to CO2 in the presence of activated sludge inoculum during a 10-day window period with ultimate biodegradability extents of 87.60% and 89.10% respectively at the end of the 28-day test duration. Whereas, the synthetic hydrocarbon fluids have longer lag phase before biodegradation began and they were only fairly biodegradable under the aerobic microbial consortium with ultimate biodegradation values of 51.85% and 62.30% at the end of the 28-days test period for SHBF and SEBF respectively.