Microbial Diversity and Potential Sulfide Producers in the Karazhanbas Oilfield (Kazakhstan)

Biogenic sulfide production in oilfields results in lower quality of oil and gas and in corrosion of oil-producing equipment. Bactericidal agents are not used at the Karazhanbas oilfield (Kazakhstan), since sulfate concentrations in both injected and formation water are low or zero. However, increasing corrosion of steel equipment and sulfide release into formation water were observed in the course of the oilfield development. The goal of the present work was to reveal the potential agents of microbial corrosion and to investigate the possibility to suppress development of sulfidogens using nitrate. Environmental conditions and the composition of microbial communities in production and injection water were studied for the sites with different temperatures. High-throughput sequencing of the V3–V4 region of the 16S rRNA gene revealed predominance of thermophilic sulfate-reducing bacteria (genera Thermodesulfobacterium, Thermodesulfovibrio, Desulfotomaculum, Thermodesulforhabdus, Desulfovirgula, Defluviitoga, and Desulfonauticus) and archaea (genus Archaeoglobus) at the high-temperature horizon, as well as of thiosulfate-reducing (genera Thermoanaerobacter, Anaerobaculum, and Coprothermobacter) and syntrophic bacteria, while abundance of methanogens (genera Methanolinea and Methanothermobacter) was low. Communities from low-temperature horizons contained mesophilic methanogens (genera Methanococcus, Methanobacterium, and Methanothrix), thermophilic and mesophilic sulfate-reducing bacteria (genera Desulfovibrio, Desulfomicrobium, Desulfosarcina, Desulfoglaeba, Desulfotignum, and Desulfocurvus), syntrophic bacteria (genus Smithella), and members of the genera Marinobacter, Paracoccus, Alcaligenes, Arcobacter, and Halomonas. Enrichment cultures of bacteria producing sulfide were obtained from formation water, as well as the cultures reducing nitrate to nitrite and suppressing growth of sulfate- and thiosulfate-reducing bacteria. These findings may indicate the possibility of using nitrate as a competitive inhibitor of sulfidogenesis in this oilfield. Corrosion-active hydrogen-utilizing methanogens and acetogens were also found, which implies the necessity for monitoring the oilfield microbial communities.