Modeling of CO2 Solubility in Salty Aqueous Solutions at Geological Sequestration Conditions

Session H5: Systems Modeling and Climate Change: A systematic Methodology for Disentangling Elements of Vulnerability, Adaptation and Adaptive Capacity

Injecting CO₂ into deep saline aquifers possesses the highest potential capacity for geological carbon storage (GCS) in order to mitigate climate change. CO₂ solubility in salty aqueous solutions plays a key role in GCS. However, the models of CO₂ solubility are scanty when the mixture of K⁺, Na⁺, Ca²⁺ and Mg²⁺ in aqueous solution is included. In this study, a simple model for CO₂ solubility is proposed covering conditions typically encountered in geological sequestration. Effect of the property and concentration of K⁺, Na⁺, Ca²⁺ and Mg²⁺ on the solubility of CO₂ is quantified based on the behavioral featers of solubility data. In order to describe CO₂-brine phase equilibrium, the Peng-Robinson equation of state (PR-EOS) and Krichevsky-Kasarnosky equation (KK equation) are applied. The (PR-EOS) is modified for better performance in high salinity brine. The Henry's constant is precisely described by temperature and concentration of the mixed ions. A linear correlation is also found between the partial molar volume of CO₂ and the ions in aqueous solution at a given temperature. The relationship can be represented by parameters optimized with least squares approach. The predicted solubility of CO₂ in pure water and aqueous NaCl solutions are well validated at the temperature and pressure ranges of 313-453 K and 8-50 MPa, where adequate experimental measurements are given. In terms of salty aqueous solutions with mixed ions, desirable agreement is achieved between this model and the literature data, making our work possess theoretical and practical significance to the GCS.