HORIZONTAL AND VERTICAL COMPARISON OF MICROBIAL COMMUNITY STRUCTURE IN LOW PERMEABILITY RESERVOIR

Petroleum microbiology is crucial in the application of Microbial Enhanced Oil Recovery (MEOR) technology. MEOR is a low-cost and environmentally friendly technique that utilizes microorganisms and their metabolites to enhance the production of oil by directly acting on the reservoir and crude oil. Through the action of microbial metabolites, the wettability of the reservoir can be altered, crude oil viscosity can be reduced, heavy components can be degraded, interfacial tension can be lowered, and oil mobility and sweep efficiency can be increased, ultimately leading to an increase in the oil recovery rate. The microbial community structure in reservoirs is complex, and due to geological variations, the community structure exhibits uniqueness. Previous studies have conducted extensive research on the microbial community structure in petroleum. However, most of these studies have focused on the changes in microbial communities in a single well, a single block, and before/after water flooding, lacking comparative studies on the in-situ microbial communities across different layers and regions. This study conducted a comparative analysis of the original microbial communities in two oil wells in the Hujianshan Oilfield, Ordos Basin, which have the same depth (Layer Chang 8) but are approximately 20 kilometers apart. In conjunction with our team's achievements in Layer Chang 4+5, we compared the differences in microbial community structures of the oil wells at both horizontal and vertical scales. The study shows that the influence of horizontal distance on microbial community structure is almost negligible within a smaller range (less than 20 km), although there are differences at larger spatial scales. However, the dominant microbial phyla (such as Proteobacteria and Actinobacteria) exhibit similarities. On the other hand, the variation in vertical depth (greater than 300 m) has a significant impact on the community, primarily controlled by temperature. As the depth increases, the temperature of the formation rises, resulting in a noticeable increase in thermophilic and anaerobic bacterial species in the community. This study enables a more targeted and detailed application of MEOR, enriching the analysis of microbial communities at a local geographic scale, and ultimately improving the success rate of MEOR.