Experimental study of microbial enhanced oil recovery and its impact on residual oil in sandstones
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The objective of this research project was to determine experimentally, using core floods, whether providing additional nutrients to accelerate the growth of nitrate-reducing bacteria alongside aerobic bacteria would result in an improved oil recovery in sandstone rocks. The hypothesis was that indigenous reservoir microbes only need additional nutrients to be able to alter the forces enacting within an oil-water-rock system drastically. As a microbial population grows, individual bacteria strains may colonize to form biofilm and produce microbial byproducts. In general, enhanced oil production from microbes can be categorized into three mechanisms, fluid diversion, interfacial tension (IFT) reduction, and solvent production. Moreover, the distribution and connectivity of the remaining oil could influence the response time and quantity of additional oil production. From the Computed Tomography experiments conducted in this study, it was made apparent that oil distribution does not change considerably when changing brine injection rate after reaching residual oil saturation. However, future experiments are recommended to determine if the waterflood flow rate before reaching residual oil saturation will influence the distribution of capillary-bound oil. Conventional Microbial Enhanced Oil Recovery (MEOR) projects involving the injection of surface-produced byproducts to release oil has proven to be costly, inefficient, and unpredictable. Recent research suggests stimulating indigenous reservoir microbes with inorganic nutrients would increase oil production in a cost-effective manner. In this study, an optimal methodology of conducting microbial corefloods with live reservoir microbes and inorganic nutrients is devised. Corefloods performed in absence of sodium dithionite had overall better microbial growth. Experiments conducted with 1% salinity brine yielded little tertiary oil production (0.1% Sor reduction). MEOR experiments in both 2.5 and 5% salinity systems showed significantly more oil release (1 to 6.5% Sor reduction). Furthermore, secondary waterflood flow rate did have an impact on the tertiary oil recovery (more than 5% difference in Sor reduction). The work presented in this study can be used as a precursor to analyze MEOR performance on high viscosity oil or in heterogeneous rocks.