Measurement and estimation of CO2–brine interfacial tension and rock wettability under CO2 sub- and super-critical conditions

Abstract

Saline aquifer storage is considered to be a promising method of carbon dioxide (CO2) mitigation. The CO2–brine interfacial tension (IFT) and the caprock wettability under reservoir temperature and pressure conditions are essential for storage capacity estimation. In this study, the CO2–brine (NaCl + KCl) IFTs were obtained by using the pendant drop method under 298–373 K temperature, 3–15 MPa pressure, and 1.0–4.9 mol·kg−1 salinity. A detailed analysis of the relationship of IFT with temperature, pressure, and salinity was conducted. In addition, an empirical equation was developed to estimate the CO2–brine IFTs in a wide range of temperatures, pressures, and salt molality. The contact angles (CAs) of brine on quartz, Berea Sandstone, and limestone surfaces in the presence of supercritical, liquid, and gaseous CO2 were measured by using the sessile drop method, and the wettability alteration of the rock surfaces in the presence of supercritical CO2 was systematically investigated. According to the results, the CO2–brine IFTs increased with salinity and temperature and decreased with pressure until reaching a plateau. For a CO2–mixed brine system, a linear relationship between the IFT increase (Δγ) and molality was observed. The CAs of the different rock samples varied with temperature and pressure. However, all the three rock samples became less water-wet when the CO2 phase state changed from subcritical to supercritical.