New correlations for interfacial tension of CO2-water-electrolyte systems at high pressure

Abstract

The CO2-aqueous phase interfacial tension (IFT) is a major property in enhanced oil recovery (EOR) processes by low salinity water alternating CO2 (CO2LSWAG) flooding. It affects oil displacement in CO2LSWAG processes as it is related to CO2 dissolution in oil through the CO2-saturated aqueous phase. Therefore, low CO2-aqueous phase IFT values are related to improvements in the oil recovery. However, the literature is still absent of simple and accurate models for IFT of CO2-water-electrolyte systems at reservoir temperature, water salinity and high pressure. Aiming to fill this gap, this work employed IFT data from the literature to present novel empirical and semiempirical correlations to calculate the IFT of these systems as a function of the phase densities at reservoir conditions, including the atypical conditions of high pressure and salinity of Brazilian Pre-Salt basin. The strategies proposed to model the phase densities when modeling the IFT through empirical and semiempirical equations are unprecedented in the literature and produced quite promising results. The results indicate that the proposed empirical equations can predict the CO2-water IFT with overall absolute deviations up to 6% over pressures between 0.1 and 45 MPa and temperatures between 30 and 75 °C. For CO2-brine systems, the proposed semiempirical equation provided an overall absolute deviation lower than 8% for brines composed of only NaCl, both NaCl and CaCl2 and only CaCl2 over 2 to 45 MPa, 40 to 75.5 °C and salinities up to 356,872 ppm. The accuracy of the proposed correlations is higher than those of the Parachor model, usually employed in commercial reservoir simulators. Also, they need lower computational efforts and can be advantageous for simulations purposes.