Thermodynamic study of the CO₂ – H₂O – NaCl system: Measurements of CO₂ solubility and modeling of phase equilibria using Soreide and Whitson, electrolyte CPA and SIT models

The thermodynamic study of the CO₂-H₂O-NaCl system is of great importance whether in an environmental context as part of Carbon Capture and Storage (CCS) or in an economic context such as enhanced oil recovery by CO₂ injection, or massive and reversible underground storage for industrial use (methanation, fermentation, water treatment, carbonation of drinks, etc.). In this work, using a new set-up based on the “static-analytic” method, measurements of CO₂ solubility in aqueous sodium chloride solution were performed at molalities between 1 and 3 m, at temperatures between 50 and 100 °C and pressures up to 230 bar. For the modeling part, an electrolyte version of the PR-CPA (Peng-Robinson Cubic Plus Association) equation of state was developed under the name “e-PR-CPA”, as well as modified Soreide and Whitson (m-SW) model was used and improved. These two models using the phi-phi approach are compared with two geochemical models (Corvisier 2013 and Duan el al. 2006) using the gamma-phi approach, and against the literature and measured data. The measured data are in good agreement with the literature data and model predictions. Under geological storage conditions, the e-PR-CPA and Duan models estimate solubility slightly better (Average Absolute Deviation less than 6.6%) than the m-SW model and the geochemical model (AAD less than 7.6%).