Challenges and distortions in microbial community analysis of oil reservoirs: a case study with heavy crude oil from the Romashkino field.

The study of the microbial community of wells is a methodologically complex, but urgent problem. In the course of our work, five samples of oil wells were selected from one deposit of the Romashkino field. The samples were subjected to nucleic acid extraction using three methods-direct DNA extraction, and after enrichment using aerobic and anaerobic cultivation methods. In three samples from wells W1-W3, extraction after anaerobic enrichment was successful. Effective aerobic cultivation was possible in all five samples. All three of these samples represented the aqueous part of the produced fluid; samples from wells W4 and W5, where extraction was difficult, represented the oil part. During the analysis of the microbial community in enrichment cultures from wells W1-W3, exogenous microorganisms such as Desulfovibrio, Acetobacterium, Bacillus, and Georgenia were discovered, which can be explained by the long-term exploitation of this section of the field. In one sample from well W1, community information was obtained using direct extraction and anaerobic enrichment. It was found that the microbial community changed significantly after enrichment, and its diversity decreased. At the same time, however, the functional profile of microorganisms has not changed, and sulfate-reducing microorganisms dominate in both samples. Thus, the results of the work allow us to make an assumption about the physicochemical parameters of samples in which the study of the microbial community is possible. In addition, it became known that well W1 needs to control the process of biological acidification and has a high risk of equipment corrosion.