Investigation of biogas for enhancing oil recovery with indigenous microorganism in high salinity oil field

Abstract

The feasibility of microbial enhancing oil recovery (MEOR) by biogas in Qinghai oil field with hypersalinity was studied. Different nutrient packages (molasses, coin milk, and starch) for biogas production were evaluated, respectively. The indigenous microorganisms preferentially use carbon source (molasses) to produce gas, and 0.9% molasses promoted the gas production effectively, the gas/liquid ratio came up to 0.775, the biogases was composed of CO2 (54.37%), N2 (45.03%), and H2 (0.60%), and pressure reached to 0.64 MPa. The effect of nitrate addition on microbial H2S production was also investigated. Addition of 0.2% nitrate led to complete elimination of sulfate-reducing bacteria. Because the microbial community significantly influences the results of the application of MEOR, so the microbial community structure dynamics was also analyzed by denaturing gradient gel electrophoresis (DGGE). Species were confirmed mainly to Halomonas sp. and some uncultured bacteria. In sand pack experiment, the acetate concentration in the experimental group achieved to 15.8 mM, and the residual oil recovery was 7.27% which exhibited a great potential to enhance oil recovery.