Anaerobic Biodegradability of Oil Base Fluid For Invert Emulsion Drilling Fluid.

Abstract

Abstract Environmental legislations restrict the use of oil based muds, specially in North Sea and their discharge under the form of oily cuttings. Different synthetic based muds (SBM) are proposed for replacing gas oil as the base fluid. These are low toxicity mineral oils, poly or mono olefins, acetals, esters… Controversial data exist concerning their biodegradability under aerobic or anaerobic conditions. Both conditions are representative of offshore drilling activities since the oil present in the cuttings deposited on the seabed can be degraded 6n the surface through oxygen process and in the center of the pile through anaerobic process. For examination of the easy and ultimate anaerobic biodegradability, the ECETOC screening test is generally employed. This procedure was here improved to evaluate the variability due to the digester sludge. The disappearance of the initial substrate is evaluated by gas chromatography analysis that gives information on the alteration of the base oil chemical structure. The potential for anaerobic biodegradability of an oleic acid ester is compared to an a olefin (C12-C14) and fructose used as a reference substrate. An important biodegradation of the oleic acid ester is observed i.e. more than 80 % of ultimate biodegradation to CO2 and CH4 and total primary biodegradability with no accumulation of the corresponding fatty acids. This attests the easy anaerobic biodegradability of the oleic acid ester In the same conditions, the test performed with the a olefin presents a low pressure evolution and low CH4 production confirming the poor anaerobic biodegradability of this type of compounds. P. 799