Analysis of microbial communities in the oil reservoir subjected to CO(2)-flooding by using functional genes as molecular biomarkers for microbial CO(2) sequestration

Sequestration of CO(2) in oil reservoirs is considered to be one of the feasible options for mitigating atmospheric CO(2) building up and also for the in situ potential bioconversion of stored CO(2) to methane. However, the information on these functional microbial communities and the impact of CO(2) storage on them is hardly available. In this paper a comprehensive molecular survey was performed on microbial communities in production water samples from oil reservoirs experienced CO(2)-flooding by analysis of functional genes involved in the process, including cbbM, cbbL, fthfs, [FeFe]-hydrogenase, and mcrA. As a comparison, these functional genes in the production water samples from oil reservoir only experienced water-flooding in areas of the same oil bearing bed were also analyzed. It showed that these functional genes were all of rich diversity in these samples, and the functional microbial communities and their diversity were strongly affected by a long-term exposure to injected CO(2). More interestingly, microorganisms affiliated with members of the genera Methanothemobacter, Acetobacterium, and Halothiobacillus as well as hydrogen producers in CO(2) injected area either increased or remained unchanged in relative abundance compared to that in water-flooded area, which implied that these microorganisms could adapt to CO(2) injection and, if so, demonstrated the potential for microbial fixation and conversion of CO(2) into methane in subsurface oil reservoirs.