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

Abstract

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.