Aerobic and anaerobic biodegradation of synthetic drilling fluids in marine deep-water offshore environments: Process variables and empirical investigations

Abstract

In this study, the aerobic and anaerobic biodegradation tendencies of a newly developed synthetic ester drilling fluid named “SEEP Mixture synthetic fluid” in marine deep-water environment were experimentally studied. The results were compared with a GTL and LASF synthetic hydrocarbon fluids. A modified Oxygen (O2) Consumption and a gas pressure measurement technique were used for biodegradation evaluation in the aerobic and anaerobic digesters respectively. The tested drilling fluids were exposed to the sea water inoculum for a period of 28 and 60 days in the different digester designs. An empirical investigation of the influence of some paramount biodegradation factors among others such as reaction temperature, dissolved oxygen concentration, time, chemical and inoculum concentrations was conducted.The biodegradation levels in SEEP mixture synthetic fluid and reference chemical sample were already above 60% during the 10-day window period under aerobic condition which shows that the new ester fluid (SEEP mixture) is inherently-readily biodegradable under aerobic condition. The ultimate biodegradability degrees of the new fluid were 81.50% and 76.10 % in aerobic and anaerobic pathways respectively. The rates of biodegradation were higher in the aerobic than in anaerobic medium in all the tested fluid chemicals. However, the GTL and LASF fluids (SHBF & SEBF) were not readily biodegradable in both microbial consortia. The rate of aerobic and anaerobic biodegradation has a positive linear relationship with incubation time and temperature but an inverse relationship with substrate concentration. Finally, Lower oxygen concentration in sea water reduces aerobic biodegradation while anaerobic transformation is grossly dependent on the availability of alternative electron acceptor ions such as NO3−, SO42−, Fe3＋ Mn4+, and CO32− and methanogens in the sea water.