AN IMPROVED TOUGH2 MODULE TO SIMULATE GEOLOGICAL CO2 STORAGE IN SALINE AQUIFERS

A new TOUGH2 module to simulate geological CO₂ storage (GCS) in saline aquifers is presented. This newly developed module is based on the widely employed ECO2N module of TOUGH2, and it accounts for the partitioning of CO₂-CH₄-H₂S-N₂ gas mixtures and brine between the aqueous and gas phases. Simple but robust thermophysical correlations are used to obtain density, viscosity, and enthalpy of the gas phase. The implementation and accuracy of the employed thermophysical correlations are verified by comparisons against the national institute of standards and technology (NIST) online thermophysical database. One-dimensional radial simulation results of CO₂ injection into a confined and non-isothermal saline aquifer obtained with the new and ECO2N modules are compared to verify the heat transfer calculations. To verify the multicomponent capability of the new module, simulation results obtained with the new module for the role of CO₂ in CH₄ exclusion from deep brine are compared against simulation results obtained with the EOS7C module of TOUGH2. Finally, to demonstrate the scope of the new module, injection of CO₂ containing H₂S as an impurity is simulated and compared against simulation results obtained with the Computer Modelling Group (CMG) reservoir simulation software. The comparisons show that the new TOUGH2 module can successfully simulate the multiphase, multicomponent, and non-isothermal flow of CO₂-CH₄-H₂S-N₂ gas mixtures and brine under a wide range of temperature, pressure, and salinity conditions. Owing to its capability to handle CO₂-CH₄-H₂S-N₂ gas mixtures and its compatibility with TOUGHREACT, this new TOUGH2 module offers the possibility of developing a new TOUGHREACT module to predict the fate of CO₂ in GCS sites under biotic conditions where CO₂, CH₄, H₂S, and N₂ gases can be formed.