Phase Equilibria of CO2-Water and CO2-Brine at High Temperatures: From Monte Carlo Simulations to the Equation of State

Accurate modeling of density and CO2 partitioning in the CO2-water and CO2-brine systems over a wide pressure and temperature range is of high interest in many subsurface processes. We parametrize a new set of CPA and eCPA equations of state accounting for the CO2-H2O cross-association. The CO2-water phase diagrams and the CO2 solubility in NaCl brine are reproduced up to 700 K and 6 m of salinity. The density of CO2 in aqueous mixtures is predicted accurately, including the effect of CO2 dissolution, which may increase or decrease the density depending on conditions. From Monte Carlo simulations, the SPCE-EPM2 force field with optimized unlike parameters reproduces the high-temperature phase diagram without polarization corrections. In this work, our knowledge of the thermodynamics of CO2 in aqueous mixtures is expanded by providing a model for geothermal and CO2 sequestration conditions.