The Impact of Sulphate-Reducing Bacteria on Corrosion and Reservoir Souring in Oil and Gas Systems

RIP2025-00018: Bacteria associated with oilfield environments are commonly observed in any context where water is present within the hydrocarbon production process. These microorganisms are key contributors to microbiologically influenced corrosion (MIC) in both wells and production facilities. Additionally, they may promote reservoir souring through the metabolic activity of sulphate-reducing bacteria (SRB), which produce hydrogen sulfide (H2S) as a by-product. Reservoir souring may also result from shifts in the fluid phase distribution and partitioning of H2S, a process by which H2S, though present from the onset of production, may initially remain undetected. Therefore, it is imperative to undertake comprehensive analysis and evaluation of the reservoir souring potential to identify the underlying causes and to formulate effective management and mitigation strategies for souring root cause and corrosion in the context of ongoing field development.

This study presents a reservoir souring risk analysis, along with an H2S forecast for an onshore oilfield in Thailand. Data were collected from over 40 distinct well and production sites, incorporating on-site sampling, laboratory analysis, historical data review, and 2D reservoir souring modeling. Microbiological status was assessed using a variety of methodologies, including Adenosine Triphosphate (ATP) bioluminescence testing, Most Probable Number (MPN) technique, quantitative polymerase chain reaction (qPCR), and the Sani-Check.

The findings revealed a high degree of bacterial diversity, with mature biofilm-forming colonies and significant populations of corrosive species. The injection water system was shown to be contaminated with bacteria, which not only persisted but also proliferated, resulting in microbial growth and biofilm accumulation in reservoir system. In combination of the abundance of carbon sources such as acetate which readily utilized by SRB suggests that the reservoir environment is conducive to microbially mediated souring. However, the progression of souring was found to be largely constrained by sulfate concentrations within the water system. The findings from this study were utilized to guide the selection of wells for biocide injection aimed at mitigating elevated surges of H2S. The implementation of this strategy proved to be highly effective, resulting in a significant reduction of H2S levels in sweet service facility design.

Furthermore, bacterial isolates from the sites were cultured in Fixed Film Upflow Bioreactors to evaluate the rate of biological H2S production and to assess the efficacy of various biocides. The results demonstrated that biocides containing 30-60% tetrakis(hydroxymethyl)phosphonium sulfate (THPS) provided superior performance, particularly against SRB, when compared to formulations based on glutaraldehyde and quaternary ammonium compounds.