A new model for the density of saturated solutions of CO2–H2O–NaCl in saline aquifers

A new model is proposed to find the density of saturated ternary solutions of H2O–CO2–NaCl in the temperature range of 50–100 °C and pressures up to 600 bar. The model calculates the partial molar volume of dissolved CO2 from the density of saturated binary, H2O–CO2, solution and the corresponding mole fraction of dissolved CO2. The density of the saturated binary solution is determined as a function of temperature and pressure from a regression of experimental data. The mole fraction of dissolved CO2 is obtained from the Redlich–Kwong equation of state. The partial molar volume of CO2 obtained in his manner is then made to coincide with one solution branch of the Redlich–Kwong equation while retaining the other solution branch associated with the molar volume of the gas phase. This allows the simultaneous calculation of both the gas and the liquid molar volume with a single equation of state. The density of the saturated ternary solution predicted by the new model is found to be in good agreement with experimental data. The new model is then used to characterize the effects of temperature, pressure and salinity on the onset of buoyancy driven convection during CO2 sequestration.