Anaerobic Microbial Activities of a Nigerian Deep Offshore Oil Production Facility that Uses High Sulfate Sea Water for Injection

Abstract

Aim: To evaluate the Anaerobic microbiological activities and souring potential of a Nigerian deep water offshore oil production facility with special emphasis on functional group activities. Methodology: CSB-K medium was used for the anaerobic microbial activity assay such as the ability to reduce sulfate by sulfate reducing bacteria (SRB), oxidize sulfide and reduce nitrate by the sulfide oxidizing, nitrate reducing bacteria (soNRB) and reduce nitrate by the heterotrophic nitrate reducing bacteria (hNRB) while API-RP-38 and ZPRA-5 broth media were used to quantify the presence of SRBs and acid producing bacteria respectively. Results: Results on the activities of anaerobic microorganisms indicated that sample 3N1(treated produced water) had the highest concentration of SRBs and Acid producing bacteria (105 and 107 cells/ml respectively), considerable concentrations of heterotrophic nitrate reducing bacteria and sulphide oxidizing nitrate reducing bacteria were also present in the same sample. The partially treated produced water samples (3N2 and 3N4) showed relatively lower concentrations of SRBs and acid producing bacteria. Expectedly very low microbial activity was recorded in the biocide treated injection water (3N3). Comparatively, the highest microbial activity on sulfide oxidation, nitrate reduction, sulfate reduction and production of hydrogen sulfide was recorded in sample 3N1 while the lowest microbial activity was recorded in sample 3N3. Conclusion: Anaerobic microbiological activities of the oil field under investigation indicate that the field have high potential for souring and corrosion due to the availability of sulfate, organic nutrients and SRBs but the operators of the field have taken measures to control souring and bio-corrosion which include periodic biocide treatment and nitrate injection.