Measurements and Modeling of Interfacial Tension for CO2/CH4/Brine Systems under Reservoir Conditions

Supercritical CO2 injection is a promising way to hydraulically fracture tight/shale gas formations as well as enhance gas recovery from these formations. Understanding of phase behavior and interfacial tension (IFT) of CO2/CH4/brine (NaCl) systems is important, because they affect the performance of such a process in tight/shale gas formations. In this study, we employ the axisymmetric drop shape analysis (ADSA) method to measure the IFT between CO2/CH4 mixtures and brine over the temperature range from 77.0 to 257.0 degrees F and the pressure range from 15 to 5027 psia. Test results show that the presence of CO2 decreases the IFT of CH4/H2O or CH4/brine (NaCl) systems, while the degree of reduction depends on the molar fraction of CO2 in the gas mixture. Salinity tends to cause an increase in IFT of CO2/CH4/brine (NaCl) systems; a higher salinity leads to an increased IFT for a given system. On the basis of the Parachor model (Weinaug and Katz J. Ind. Eng. Chem. 1943, 35, 239) and Firoozabadi's model (Firoozabadi and Ramey J. Can. Pet. Technol. 1988, 27, 41), we propose an improved IFT model to represent the measured IFT data for CO2/CH4/brine systems. The new IFT model preserves the principle of zero IFT at a critical point. Comparison of the new IFT model with four commonly used IFT correlations presented in the literature shows the superiority of the new model.