A simple model for the prediction of CO₂ solubility in H₂O-NaCl system at geological sequestration conditions

Carbon dioxide (CO₂) released in the atmosphere is the principal cause of the so-called global warming or greenhouse phenomenon. One procedure for the mitigation of CO₂ consists of the capture, transport and geological storage (sequestration) of the gas in deep saline aquifers. In this work, a model for predicting CO₂ solubility in H₂O-NaCl system covering conditions typically encountered in geological sequestration (e.g., 300-500 K, 50-2000 bar, and 1-4 mol salt/kg) has been developed and validated by comparison with available experimental and theoretical data. Themodel is a simple one with four adjustable parameters that is based on an extension of the well-known Setschenov model [K_gs /K_g0=(P/P₀)f(T_r,m) with f(T_r,m)=(0.461+0.078 m) (-1+T_r/(1.0+0.1267 m)]. The model is developed by exploiting interesting features in the behavior of solubility data of CO₂ in saline water over the above-mentioned ranges of conditions. The model is capable of predicting CO₂ solubility in saline water with accuracy comparable to that made by multi-parameter models (having 20 parameters or more). It is also in very good agreement with the available experimental data with root-mean-squared-error (RMSE) in the range of 0.03-0.225 mol CO₂/kg H₂O. The extrapolative power of the model is acceptable at both ends of its range of applicability.