Microbial communities in crude oil phase and filter-graded aqueous phase from a Daqing oilfield after polymer flooding

Aims The aim was to characterize indigenous micro-organisms in oil reservoirs after polymer flooding (RAPF). Methods The microbial communities in the crude oil phase (Oil) and in the filter-graded aqueous phases Aqu0.22 (>0.22 mu m) and Aqu0.1 (0.1-0.22 mu m) were investigated by 16S rRNA gene high-throughput sequencing. Results Indigenous micro-organisms related to hydrocarbon degradation prevailed in the three phases of each well. However, obvious differences in bacterial compositions were observed amongst the three phases of the same well and amongst the same phase of different wells. The crude oil and Aqu0.22 shared many dominant bacteria. Aqu0.1 contained a unique bacterial community in each well. Most bacteria in Aqu0.1 were affiliated to culturable genera, suggesting that they may adapt to the oil reservoir environment by reduction of cell size. Contrary to the bacterial genera, archaeal genera were similar in the three phases but varied in relative abundances. The observed microbial differences may be driven by specific environmental factors in each oil well. Conclusions The results suggest an application potential of microbial enhanced oil recovery (MEOR) technology in RAPF. The crude oil and Aqu0.1 contain many different functional micro-organisms related to hydrocarbon degradation. Both should not be overlooked when investing and exploring the indigenous micro-organisms for MEOR. Significance and Impact of the Study This work facilitates the understanding of microbial community structures in RAPF and provides information for microbial control in oil fields.