Microbial Diversity of Reservoir Water from the Biklyanskoe Oil Field Used for CO2 Sequestration

The sequestration of carbon dioxide in depleted oil reservoirs is one of the ways to achieve zero emissions into the atmosphere This technology could become even more attractive if the sequestered carbon dioxide is reduced to methane by subsurface methanogenic archaea. The purpose of this work was to determine the physicochemical conditions and composition of the microbial community at the Biklyanskoe oil field before and after CO2 injection. The oil reservoir is characterized by an extremely high total mineralization of reservoir water (179.3 to 292.1 g L−1). Using high-throughput 16S rRNA gene V3–V4 fragments sequencing, aerobic organotrophic (genera Pseudomonas, Acinetobacter, Arcobacter, Thauera, and Sphingomonas), fermentative (Proteiniphilum, Anaerolinea, and Thermovirga), and sulfate-reducing bacteria (Desulfovermiculus and Desulfotignum), and methanogenic archaea (Methanohalophilus, Methanomethylovorans, and Methanosarcina) were detected in reservoir water and enrichment cultures. While CO2 injection did not lead to an increase in the number of fermentative and methanogenic prokaryotes in reservoir water, a decrease in pH, an increase in total mineralization, and in the concentration of calcium, magnesium, and bicarbonate ions revealed in the formation water were probably due to chemical processes. It is necessary to search for cheap processes/conditions/chemicals so that the process of bioconverting CO2 to methane can be effective.