Microbial and Geochemical Characterization of Wellington Oil Field, Southcentral Kansas, and Potential Applications to Microbial Enhanced Oil Recovery

Abstract

The aqueous geochemistry and microbiology of subsurface environments are intimately linked and in oil reservoir fluids. This interdependence may result in a number of processes including biodegradation of oil, corrosion of pipes, bioclogging of porous media, and biosurfactant production. During production of oil and reinjection of production water, surface exposed fluids are introduced to oxygen and exogenous microbes, both of which may alter reservoir biogeochemistry. In this study, production waters from six wells within the Wellington Field in SE Kansas, which has been water flooded continuously for 60 years, were sampled and analyzed for geochemistry, microbial ecology, microbial biomass, and biosurfactant production to better understand the relationship between the microbiology and oil production in the field. Minor differences in aqueous geochemistry were detected among the five production wells and single injection well, and data analysis and modeling indicate that depth-specific water-rock reactions play a major role in controlling the major ion geochemistry in the field. Microbial diversity in fluids produced from the wells indicated a system that is in steady state, with microbial community composition linked to the stratigraphic location of pumping rather than injection of recycled fluids. Further, analyses of surface tension, a proxy for biosurfactant production, and its relationship to microbial biomass and oil production, suggests that while biosurfactants may be produced, biomass is likely clogging porosity and inhibiting oil recovery. Biociding practices, the injection of chemicals toxic to microorganisms, are implemented in the Wellington field to keep microbial biomass low. This study suggests their effectiveness may need to be addressed further. Known biosurfactant-producing microbes isolated in this study may be targeted for in-situ stimulation to increase biosurfactant production through the introduction of nutrient and energy sources into the reservoir that can increase oil production.