Whole metagenome of injected and produced fluids reveal the heterogenetic characteristics of the microbial community in a water-flooded oil reservoir

Abstract

In order to understand the subsurface microbial community and how it functions in a water-flooded reservoir, the whole metagenome of fluids from production and injection wells were sequenced using next-generation sequencing and then compared. Gene function was annotated by the Kyoto Encyclopedia of Genes and Genomes (KEGG), evolutionary genealogy of genes: Non-supervised Orthologous Groups (eggNOG) and hydrocarbon degradation databases. More biomass was detected in fluid from the injection well than in the production well. As a typical water-flooded reservoir, injection and production communities were dominated by Proteobacteria. In the production metagenome, more genes involved in denitrification and hydrocarbons utilization pathways, reflecting the strict anaerobic and oil-rich conditions in reservoirs. The higher abundance of genes responsible for methyl chemotaxis, aerotaxis and flagella indicate that the community in reservoirs is motivated to access limited nutrients and electron acceptors. Combined with knowledge of porous flow, these metagenome results indicate that the microbial communities detected in produced fluids are actually derived from different habitats in the reservoir, which are established by the chromatographic effect of reservoir flooding. Furthermore, diverse flow patterns at pore scale could affect in situ proliferation and syntrophy between species, which could considerably shift the microbial composition in produced fluids.