CO2 solubility in brine is sensitive to ions as several complexes may result from geochemical reactions. Recent experiments show difference in solubility for brine solutions with equal ionic strength but different salts (NaCl, CaCl2 and KCl). Hence, current methods that incorporate the effect of ions solely by measuring the ionic strength are inadequate to model CO2 solubility in brine.
In this research, a new solubility model that accounts for the presence of particular ions has been developed using the Gibbs free energy minimization model. The Gibbs free energy function provides the advantage of combining different thermodynamic models - Equation of State (EOS) for hydrocarbon or gas phase components and activity coefficient model for aqueous phase components. The developed model uses Pitzer activity coefficients for aqueous phase components where experimental data available for individual salt mixtures have been used to tune coefficients. We use this solubility model to quantify the impact of particular ions for CO2 sequestration application. We discuss strategies for modifying the brine composition that can increase CO2 solubility and hence, aid CO2 sequestration.