Interfacial tension of CO2Â +Â brine systems: Experiments and predictive modelling

In this study the interfacial tension (IFT) between CO2 and brines, in the context of geological storage of CO2, was investigated. Investigations covered both experimental and theoretical aspects of this property over a broad range of conditions, including those found in subsurface formations. Measurements for CO2 + NaCl(aq) systems, of salt molalities 0.98 and 1.98 mol.kg-1, were performed for temperatures and pressures up to 423 K and 69.51 MPa, respectively. Results clearly showed an increase from CO2 + H2O IFT upon the addition of the salt, helping to resolve some discrepancies observed in literature data. Furthermore, a predictive method, based on the Density Gradient Theory, was extended to CO2 + brine systems, with modelled IFT values yielding a good agreement with experiments from this work and literature for brines of single and mixed salts, including NaCl, KCl and CaCl2, and ionic strength up to 2.7 mol.kg−1.