TOUGHREACT-CO2Bio – A new module to simulate geological carbon storage under biotic conditions (Part 2): The bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures

Abstract

The capabilities of TOUGHREACT-CO2Bio to simulate the multiphase flow of CO2-CH4-H2-H2S gas mixtures and brine in deep geological formations were presented in Shabani and Vilcáez (2019) [Journal of Natural Gas Science and Engineering. 63, 85-94]. Here we present the capabilities of CO2Bio to simulate bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures and brine in depleted oil reservoirs under biotic conditions where CO2 and/or crude oil can be converted to CH4. In CO2Bio, the microbial production/consumption of gases (CO2, CH4, H2, and H2S) is coupled with the multiphase flow of CO2-CH4-H2-H2S gas mixtures and brine through a sequential iterative method. The kinetic model used to represent rates of crude oil biodegradation and microbial production/consumption of gases accounts for the different response of microbial species to changes in pH derived from the dissolution of CO2 into the aqueous phase and water-rock reactions. To verify the microbial capabilities of CO2Bio, we simulate batch experiments conducted to analyze the stimulation effect of CO2 and a nutrient package on the microbial conversion of CO2 and crude oil to CH4. To confirm the capabilities of CO2Bio to simulate the multiphase bio-geochemical reactive transport of CO2-CH4-H2-H2S gas mixtures and brine in deep geological formations under biotic conditions, we conducted a 3D field-scale simulation of alternate injection of CO2 and produced water into a section of the Cushing oilfield of Oklahoma. Overall, simulation results show that CO2Bio can simulate the complex multiphase-multicomponent reactive transport of CO2-CH4-H2S-H2 gas mixtures and brine under biotic conditions.