Measurement and modeling of CO₂ solubility in natural and synthetic formation brines for CO₂ sequestration

CO₂ solubility data in the natural formation brine, synthetic formation brine, and synthetic NaCl+CaCl₂ brine were collected at the pressures from 100 to 200 bar, temperatures from 323 to 423 K. Experimental results demonstrate that the CO₂ solubility in the synthetic formation brines can be reliably represented by that in the synthetic NaCl+CaCl₂ brines. We extended our previously developed model (PSUCO2) to calculate CO₂ solubility in aqueous mixed-salt solution by using the additivity rule of the Setschenow coefficients of the individual ions (Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl^-, and SO₄^2-). Comparisons with previously published models against the experimental data reveal a clear improvement of the proposed PSUCO2 model. Additionally, the path of the maximum gradient of the CO₂ solubility contours divides the P-T diagram into two distinct regions: in Region I, the CO₂ solubility in the aqueous phase decreases monotonically in response to increased temperature; in region II, the behavior of the CO₂ solubility is the opposite of that in Region I as the temperature increases.