Experimental and modelling study of the solubility of CO₂ in various CaCl₂ solutions at different temperatures and pressures

Study of the thermodynamic behaviour of CaCl₂-H₂O-CO₂ systems is important in different scientific areas in the chemical and petroleum engineering fields. For example, a system including salt-H₂O-CO₂ is a common system in CO₂ geological storage. During carbonate matrix acidizing, this mixture also appears as the spent acid. Hence, study of the behaviour of this system and the solubility of CO₂ in CaCl₂ brine in different thermodynamic conditions is critical.

In this study, CO₂ solubility in 0, 1.90 and 4.80 mol/L CaCl₂ solutions at 328.15 to 375.15 K and 68.9 to 206.8 bar were measured. These values are normal for oil reservoirs. A popular thermodynamic model is available in the literature for estimating the CO₂ solubility in pure water and NaCl solutions. In this paper, the available model was modified by experimental work to be applicable for CaCl₂ as well. Based on the measured data, the component interaction parameters in the base model were adjusted for a CaCl₂-H₂O-CO₂ system. The developed model could predict CO₂ solubility in different conditions with remarkable accuracy, particularly for high concentration solutions and at high pressures. This improvement is up to 65% better than in the base model. This model can be used in Darcy scale models for predicting wormhole propagation during carbonate matrix acidizing.