Anaerobic Microbial Activities of a Nigerian Onshore Oil Production Facility that Uses Underground Water with Zero Sulfate Concentration for Injection

Abstract

Aim: To evaluate the anaerobic microbial activities and souring potential of a Nigerian onshore oil production facility that uses zero sulfate underground water for injection. Methodology: Key functional group activities such as the ability to reduce sulfate and generate sulfide by sulfate reducing bacteria (SRB), the ability to reduce nitrate to nitrite by the heterotrophic nitrate reducing bacteria (hNRB) and the ability to reduce nitrate and oxidize sulfide by sulfide oxidizing, nitrate reducing bacteria (so-NRB) were determined in samples using CSB-K medium. Results: Lactate utilizing SRBs and hNRBs were found to be common in most oil field samples while the activities of so-NRBs were limited to very few samples. It was also observed that the underground water with zero sulfate concentration and negligible microbial activity poses no souring risk to the oil field under investigation. The produced water and oil samples from the facility though with considerable populations and activities of SRBs also recorded negligible concentration of sulfate and some organic nutrients and therefore are not likely to pose some souring risks to the oil facility under investigation. Conclusion: From our investigation, it is evident that the zero sulfate underground water with negligible SRB populations and activities poses no souring risks to the facility under investigation but corrosion risks cannot be completely ruled out since some methanogens that are indigenous to the oil field can initiate corrosion using alternative pathways in the absence of sulfate.