Phase Behavior Modeling for Carbon Dioxide/Brine Mixtures Using PR EOS and Huron-Vidal Mixing Rule

Abstract

Abstract Accurately predicting CO2 solubility in saline aquifers is very important for CO2 capture and storage. A reliable and accurate thermodynamic model is needed to predict the phase equilibrium of the CO2+brine systems over a wide range of temperature, pressure, and molality. In this study, a cubic-EOS-based thermodynamic model is presented to predict the phase equilibrium of CO2+brine mixtures. Peng-Robinson equation of state and Huron-Vidal mixing rule are applied to predict the phase behavior of CO2+brine systems containing salt species including NaCl, KCl, CaCl2, and MgCl2. Binary interaction parameters for specific CO2+single-salt+H2O systems are established as functions of temperature and salt molality. To investigate the impact of multiple salts mixtures on CO2 solubility in brine solutions, the model is extended to CO2+mixed-salt+H2O systems under the practical geological conditions (273–550K, 0–800 bar, 0–6 mol/kg). PR EOS with a modified BIP model in the HV mixing rule is implemented to capture the phase compositions in vapor-liquid equilibria (VLE). The collected experimental data are used to determine the optimal BIP model. Comparison of the experimental data and the computed data indicates that the average absolute deviation (AAD) in reproducing the CO2 concentration in the mixed-salt brine is 0.0015. Compared to other state-of-the-art models in the literature, the new model can more accurately predict the VLE of CO2+brine systems over a large temperature, pressure, and molality range.