Microbial characteristics and potential mechanisms of souring control for a hypersaline oil reservoir

The production of hydrogen sulfide (H₂S) had caused huge economic losses and security risks to oil fields, which had attracted the attention of many researchers. Studies focused on hypersaline oil reservoirs were scarce. Here, we simulated H2S inhibition by adding NO₃^- and NO₂^- in anaerobic bottles and up-flow sand-packed bioreactor in the laboratory using water samples from injection wells in the Jianghan reservoir. The microbial characteristics, pH, salinity, sulfate, sulfide, NO₃^- and NO₂^- were measured at every stage. The content of H₂S and elemental sulfur (S0) gradually reduced to 0 mg/L with injected 400 mg/L of NO₃^- and 300 mg/L of NO₂^-. Halophilic nitrate-reducing bacteria (NRBs) related to Halomonas and Arcobacter could suppress the activity of sulfate-reducing bacteria (SRBs) through the accumulation of nitrite toxicity and the competition of organic substrates with SRBs. When SRBs activity could not be suppressed, the sulfur-oxidizing bacteria related to Sulfurimonas, Thiomicrospira and Acrobacter were accumulated for souring control through microbial sulfur cycle of H₂S production and oxidation. Salinity could be a key parameter affecting microbial development and interactions. This study provides a fundamental data to souring control in the hypersaline oil reservoir by reinjection produced water amended with NO₃^- and NO₂^-.