Interfacial wettability evolution in underground hydrogen storage: Key factors, multiscale effects, and challenges

Large-scale underground hydrogen storage (UHS) has emerged as a crucial strategy for mitigating fluctuations in hydrogen demand. Wettability at the hydrogen-fluid-rock interface is a critical factor controlling hydrogen storage capacity and recovery efficiency. This review systematically elucidates the evolution of multiphase interfacial wettability during hydrogen storage, covering reservoir types, characterization techniques, key influencing factors, and their multiscale impacts. 4D X-ray microscopy offers a promising approach for characterizing the dynamic evolution of interfacial wettability under in-situ conditions. The review provides an in-depth discussion of the factors governing wettability, including geological media, gas composition, salinity, bubble size, temperature, pressure, microorganisms, and organic acids. There is currently a lack of research on the evolution of interfacial wettability under the coupled influence of multiple factors. It is worth noting that nanofluids hold significant potential for wettability control. The discussion spans from the molecular to the macro scale, detailing how the evolution of interfacial wettability impacts adsorption, saturation, gas column height, and relative permeability modeling. The coupled interaction between interfacial wettability and dynamic behavior exerts a complex influence on hydrogen saturation. Macro-scale simulation of UHS requires incorporating mixed wettability into the relative permeability hysteresis model. This review provides fundamental insights into the evolution of interfacial wettability, offering guidance for enhancing the safety and efficiency of UHS.