Multiscale wettability characterization under CO2 geological storage conditions: A review

The wettability of porous media strongly affects the trapping mechanism and storage capacity during CO2 geological storage. Various novel measuring methods have been proposed recently with the development of imaging techniques. This review describes the state-of-the-art wettability characterization at different scales in three aspects: conventional laboratory-based contact angle characterization to analyze the porous external surface properties, pore-scale contact angle analysis to summarize the wettability of the porous inner surface based on micromodels and X-ray microtomography, and overall wettability evaluation through nuclear magnetic resonance and thermodynamic contact angle and topology analysis. The impact of the pore structure, mineral composition, and surface roughness on pore-scale wettability is described, including contact angle hysteresis and mixed wettability. The wettability in various pore events and wettability alternation with various storage conditions and fluid displacement patterns provide a description of reservoir properties. This review also illustrates the feasibility of multiscale wettability descriptions. Future studies should focus on the interrelation among the contact angles at different scales. How the contact angle of a porous surface, especially at the pore scale, changes under reservoir conditions and the mechanism of wettability alternation still need to be further investigated. Additionally, the impact of rock wettability on storage capacity in practical applications is concluded. Future research will focus on methods to control wettability in actual storage sites to enhance economic benefits and ensure safety.