BIODEGRADATION OF SYNTHETIC DRILLING MUD BASE FLUIDS IN GULF OF MEXICO DEEP-SEA SEDIMENTS

Deborah J. Roberts*
David Herman
Divya Gangumalla
Veysel Demir

University of Houston
Department of Civil and Environmental Engineering
N107 Engineering Building 1
University of Houston
Houston, TX 77204-4003
Voice: 713-743-4281
Fax: 713-743-4260
E-mail: djroberts@uh.edu

Drilling of oil exploration wells beneath the sea floor requires a drilling mud that can lubricate the drill bit, carry rock cuttings to the surface, and control reservoir pressure. One component of drilling mud is synthetic base fluids (SBF), which are non-aqueous phase, olefin-based or ester-based liquids. After separation from the drilling mud, drill cuttings contaminated with residual SBF are discharged to the sea floor. We will present evidence of anaerobic biodegradation of surrogate SBF compounds in sediment collected from beneath drilling platforms in the Gulf of Mexico. Biodegradation experiments were performed under environmentally relevant conditions of low temperature (4°C) and high hydrostatic pressure (between 97 and 786 psi, depending on the depth of sampling). The ability to degrade the surrogate SBF was linked to prior exposure of the sediment to cuttings discharge. Microbial characterization of the sediment will also be presented. Experimental data will be used to complete a model which estimates the response and recovery of cuttings-impacted sediment based on microbial response, environmental conditions, and SBF chemical properties.