Assessment of CO2/shale interfacial tension

Abstract Caprocks/ CO 2 interfacial tension ( γ sc ) is an essential parameter that helps to provide insights into the interaction between CO 2 and caprocks. Lower values of γ sc suggest stronger CO 2 - caprocks interaction (lower CO 2 capacity 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 CO 2 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/ CO 2 interfacial tension ( γ sc ) in caprocks is highly dependent on total organic carbon (TOC) percentage, pressure, and quartz content. γ sc in sample-2 of higher TOC and quartz (TOC =0.11 wt%, quartz = 62%) is lower than γ sc 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 CO 2 . Lower interfacial tension implies a stronger affinity of CO 2 towards caprock surface (the high chance that CO 2 will enter through caprocks and causes leakage). Therefore, it can be inferred that high TOC caprocks offer a lower CO 2 trapping integrity, hence reducing their CO 2 storage capacity. A remarkable relationship between solid/ CO 2 interfacial tension and CO 2 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.