Molecular and cultural evidence of corrosive microorganisms in an offshore oil field in the Arctic (Russia)

The use of seawater with a high sulfate content for water-flooding of oil reservoirs contributes to the growth of sulfate-reducing bacteria (SRB), producing sulfide, which causes oil souring, corrosion of steel equipment, and environmental problems during oil production and refining. The purpose of this work was to determine the composition of microorganisms and the physicochemical parameters of the production and injection water of the Prirazlomnoye offshore high-temperature oil field in order to improve our understanding of the corrosion-active microorganisms. High-throughput sequencing of V3-V4 fragments of the 16S rRNA gene, quantitative PCR of bacteria and archaea, and cultural and analytical methods were used in the work. SRB, fermentative and syntrophic bacteria, and methanogenic archaea capable of participating in the processes of general and pitting corrosion of steel equipment were found in water samples. The production water contains sulfate, sulfide, and thermophilic SRB (<i>Thermacetogenium</i> and <i>Desulfonauticus</i>). Mixing of the produced water with seawater leads to its cooling and emergence of mesophilic SRB (<i>Desulfobacter</i> and <i>Desulfogranum</i>) in the water treatment system. Residual oil hydrocarbons and sulfides can be oxidized in the water treatment system, and the resulting metabolites serve as electron donors and acceptors for fermentative sulfidogenic bacteria (genera <i>Caminicella</i>, <i>Kosmotoga</i>, <i>Petrotoga</i>, and <i>Geotoga</i>). Sulfate-reducing and methanogenic enrichments from reservoir water produce sulfide and methane, respectively, receiving electrons from Fe⁰ in the absence of other sources of H₂, which can contribute to pitting corrosion. This study allows for improving the ways to control sulfidogens and expands understanding of the microbial diversity of oil reservoirs.IMPORTANCEOil production from oil reservoirs with sulfate-containing formation water and injection seawater is accompanied by the appearance of sulfide in oil production, which increases the cost of oil refining and enhances corrosion processes of steel equipment. In this work, the physicochemical conditions and the composition of microorganisms in the produced and injected seawater at the Prirazlomnoye oil field (Russia) are investigated. The biocides used at the oil field are ineffective in suppressing sulfate-reducing bacteria (SRB), which are considered the main agents of microbial corrosion. It has been shown that not only SRBs but also fermenting bacteria inhabiting the oilfield were capable of producing sulfide. Enrichment cultures of autotrophic SRBs and methanogens capable of receiving electrons directly from Fe⁰ with the production of sulfide and methane, respectively, were obtained. The new scientific information obtained on microbial communities of oil reservoirs will make it possible to improve methods for monitoring corrosive microorganisms and selecting biocides.