A NEW TOUGHREACT MODULE TO SIMULATE GEOLOGICAL CARBON STORAGE UNDER BIOTIC CONDITIONS

A new TOUGHREACT module, named CO2Bio, will be introduced. This module can be used to simulate the microbial conversion of CO₂ and crude oil to CH₄ in deep saline aquifers and depleted oil reservoirs. Because the biogenic conversion of CO₂ to CH₄ involves the continuous production and consumption of H₂, the capabilities of a solubility model capable of predicting the mutual solubility of CO₂-CH₄-H₂S gas mixtures and brine has been extended to account for the mutual solubility of H₂ and brine. Therefore, CO2Bio can handle the non-isothermal multiphase flow of CO₂-CH₄-H₂S-H₂ gas mixtures and brine at deep geological formation conditions. Simple but robust correlations are employed in CO2Bio to calculate thermophysical (density, viscosity and enthalpy) properties of CO₂-CH₄-H₂S-H₂ gas mixtures. The implementation and accuracy of the employed thermophysical correlations are verified by comparisons against the National Institute of Standards and Technology online thermophysical database. To verify the multiphase flow capabilities of CO2Bio, simulation results obtained using the CO2Bio module of TOUGHREACT are compared against simulation results obtained using the ECO2N module of TOUGHREACT and the EOS7C module of TOUGH2. Simulated scenarios include the injection of CO₂ into a radial infinite acting reservoir, and the extraction of dissolved CH₄ from water by injecting CO₂. To verify the field-scale applicability of CO2Bio, the alternate injection of CO₂ and brine into a reservoir, where the supply of nutrients is assumed to result in the stimulation of the microbial production of H₂ and CH₄ from the degradation of crude oil, is simulated using CO2Bio. All simulation results confirm that TOUGHREACT-CO2Bio can successfully predict the multiphase flow of CO₂-CH₄-H₂S-H₂ gas mixtures and brine.