Effects of oxygen injection on oil biodegradation and biodiversity of reservoir microorganisms in Dagang oil field, China

•Oxygen injection could change the biodiversity of reservoir microorganisms.•Reservoir microbes could degrade n-alkanes completely and PAHs partially.•Activation of reservoir microorganisms could enhance oil recovery.•This method represents a vital role in oil spill remediation.

Effects of oxygen inoculation were investigated on oil biodegradation and biodiversity of reservoir microorganism in Dagang oil field. The biodegrading was evaluated and analyzed or estimated by using in-vitro enrichment, denaturing gradient gel electrophoresis, real time PCR and GC–MS. The bacterial communities of production water containing reservoir microorganism were 30% lower than groundwater and injection water despite that all of them have rich biodiversity. After thirty days of oxygen treatment the n-alkanes degradation were 92.5% in injected water while 44.3% in groundwater and 92.4% in production water. The selected PAHs biodegradation rate in production water was lower as compared to the injection water but significantly higher than groundwater. The total bacterial biomass gradually increases after the oxygen injection and then decreases. The results suggested that aerobic condition could accelerate petroleum biodegradation and changes the microbial community structure in oil reservoir, which might be beneficial to MEOR.