2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 271-8
Presentation Time: 10:20 AM

MICROBIAL METHANOGENESIS IN OIL RESERVOIRS SUBJECTED TO THE INJECTION OF CO2


VILCAEZ, Javier, Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078, vilcaez@okstate.edu

Geochemical evidences showing that 1) CH4 is a major end product of oil biodegradation in oil reservoirs, and 2) over 20% of Earth’s biogenic CH4 have been formed by methanogenic microbes via the reduction pathway of CO2 with H2, suggest that the combined injection of CO2 and stimulating nutrients should result in the biogenic conversion of oil and CO2 to CH4 by indigenous microbes. To prove this hypothesis, batch experiments have been carried out using a mixture culture of H2-using methanogenic microbes and H2-forming fermentative microbes. It has been found that moderate acidic pH levels and the addition of protein-rich matter stimulates the biogenic formation of CH4 via the reduction pathway of CO2 with H2. To assess the feasibility of microbial methanogenesis in geological CO2 storage sites subjected to the injection of CO2 and stimulating nutrients, multiphase reactive transport simulations of microbial methanogenesis have been performed using a reactive transport model that accounts for 1) water-rock geochemical reactions, 2) microbial competition between methanogenic microbes and sulfate reducing bacteria (SRB) for H2 and acetate, and 3) the effect of pH on the activity of the microbial community. Simulation results indicate that oil reservoirs containing calcite in the mineral phase and low concentrations of sulfate in the formation water are most suitable for microbial methanogenesis from CO2 in geological CO2 storage sites. On the basis of these preliminary experimental and numerical simulation studies, in this presentation the feasibility of stimulating the microbial methanogenesis from CO2 and oil in depleted oil reservoirs will be discussed. The concretization of this possibility can result in the attenuation of the depletion of fossil energy resources and reduction of CO2 emissions into the atmosphere.