Assessment of CO2/shale interfacial tension

Caprocks/CO2 interfacial tension (γsc) is an essential parameter that helps to provide insights into the interaction between CO2and caprocks. Lower values of γsc suggest stronger CO2- caprocks interaction (lower CO2capacity is inferred) and vice versa. Rocks/CO2 interfacial tension also explains why different minerals have different wettability to CO2 at the same pressure and temperature. Two caprock samples acquired from a potential CO2 storage site in New South Wales in Australia were used in this work. All the laboratory measurements were conducted at varying pressure from 5 MPa to 20 MPa and a temperature of 343 K. Our findings suggest that solid/CO2 interfacial tension (γsc) in caprocks is highly dependent on total organic carbon (TOC) percentage, pressure, and quartz content. γsc in sample-2 of higher TOC and quartz (TOC =0.11 wt%, quartz = 62%) is lower than γsc in sample-1 of lower TOC and quartz (TOC =0.081 wt%, quartz = 31%. The higher percentage of TOC and quartz increases the hydrophobic sites available in the sample, allowing stronger affinity towards CO2. Lower interfacial tension implies a stronger affinity of CO2 towards caprock surface (the high chance that CO2 will enter through caprocks and causes leakage). Therefore, it can be inferred that high TOC caprocks offer a lower CO2 trapping integrity, hence reducing their CO2 storage capacity. A remarkable relationship between solid/CO2 interfacial tension and CO2 density–which is easy to determine – at different pressures (up to 20 MPa) and 343 K temperature was also demonstrated in this work. This insight can significantly enhance Carbon Geosequestration processes' fundamental understanding.