A Marine Anaerobic Biodegradation Test Applied to the Biodegradation of Synthetic Drilling Mud Base Fluids

Abstract

This manuscript describes a marine anaerobic biodegradation test and its application to testing the relative biodegradability of ester and olefin synthetic base fluids (SBF) for drilling mud. The test uses marine sediments spiked with the test SBF and incubated anaerobically in closed serum bottles. The production of gas (CO2 and CH4) from the sediment was used to monitor the progress of biodegradation. Gas production was a good estimation of compound biodegradation since the system was driven to methanogenesis due to the high concentrations of compounds used in the test. The degradation of esters was generally complete by 90 days of incubation, while the degradation of olefins could take more than 9 months of incubation. The source of marine sediment was very important; controlling the time it took for the test to go to completion. A sediment that had approximately 6.2% volatile solids, an esterase activity of 0.01 Δ OD490 min−1 g dry sediment−1 and > 109 MPN g dry sediment−1 sulfate reducing bacteria, > 105 MPN g dry sediment−1 methanogens, and > 108 MPN g dry sediment−1 general anaerobes was shown to provide the shortest incubation time for the degradation of olefin compounds. Sediment could be stored for up to 14 months and still pass the criteria set for a good test.