Role of Microorganisms in Oil Reservoir Souring and Its Mitigation Strategies

Abstract

Petroleum microbiology offers substantial environmental and industrial benefits by harnessing the natural capabilities of microbes to interact with crude oil and refined petroleum products. Microorganisms are found worldwide in oil reservoirs, where they degrade the oil and alter its quality. Oil reservoirs are challenging environments for microorganisms due to their high toxicity, hydrophobicity, low water activity, and extreme conditions, including high temperature, salinity, and pressure. Despite these harsh factors, oil reservoirs host a diverse range of bacteria and archaea, including fermenters, acetogens, methanogens, and organisms that reduce sulfate, nitrate, and iron. It is crucial to understand the microbiology of oil reservoirs, as oil remains one of the most vital resources for industry and energy. Sulfate-reducing bacteria (SRB) convert sulfate to sulfide, a hazardous and corrosive compound that impacts metallurgy, capital and operating costs, and operational safety. Reservoir souring is the process where a reservoir that previously did not contain any hydrogen sulfide (H2S) begins to produce sour fluids containing H2S due to microorganisms. The genetic, enzymatic, and physiological aspects of the sulfate-reduction process have been extensively studied in pure cultures in laboratory settings. Furthermore, advancements in DNA sequencing have identified new groups of microorganisms, including archaea, that can contribute to reservoir souring. Reservoir souring is primarily caused by sulfate reducing microorganisms, which leads to the formation of H2S in oil reservoirs during water flooding, although both biotic and abiotic processes are involved. This review discusses the occurrence of reservoir souring due to specific types of sulfate-reducing microorganisms and outlines strategies for managing this issue through the injection of various chemicals. In addition, the manuscript provides useful insights that can guide future research and improve reservoir management practices in the oil and gas industry.