An improved model for calculating CO2 solubility in aqueous NaCl solutions and the application to CO2-H2O-NaCl fluid inclusions

•An improved model for CO2 solubility in aqueous NaCl solutions is developed.•The solubility model is applied to CO2-H2O-NaCl fluid inclusions.•An iterative approach is presented to calculate CO2 content of CO2-H2O-NaCl inclusion.•Volume fraction and homogenization pressure can be obtained with this method.

To determine compositions, homogenization pressures and isopleths of CO2-H2O-NaCl fluid inclusions, an improved activity-fugacity model is developed to calculate CO2 solubility in aqueous NaCl solutions. The model can predict the CO2 solubility in aqueous NaCl solutions from 273.15 K to 723.15 K, from 1 bar to 1500 bar and from 0 to 4.5 mol kg− 1 of NaCl, within or close to experimental uncertainties. Compared to a large number of reliable experimental solubility data available, the average absolute deviation is 4.62% for the CO2 solubility in aqueous NaCl solutions. In the near-critical region, the calculated CO2 solubility deviations increase to over 10%. The CO2 solubility model, together with the updated volumetric model of CO2-H2O-NaCl fluid mixtures, is applied to calculate the CO2 contents, homogenization pressures, molar volumes and volume fractions of the CO2-H2O-NaCl fluid inclusions by an iterative method based on the assumption that the volume of an inclusion keeps constant during heating and cooling. Calculation program code of the CO2 solubility in aqueous NaCl solutions can be obtained from Chemical Geology or the correspondence author (maoshide@163.com).