Caprock wettability is a fundamental control on the sealing capacity and integrity of subsurface energy storage systems. In CO₂ geological sequestration, a strongly waterwet caprock ensures high capillary entry pressures, effectively preventing CO₂ migration. However, increased pressure and brine salinity can weaken hydrophilicity and compromise long-term sealing. In underground hydrogen storage, caprocks generally remain waterwet, yet the high diffusivity of H₂ reduce capillary sealing efficiency and may induce wettability alteration due to microbial or redox processes. Repeated injection-withdrawal cycles further cause transient wetting-drying and hysteresis, altering interfacial structures and capillary behavior. Understanding these dynamic wettability responses under varying physicochemical conditions is crucial for assessing storage security. Future studies should integrate in-situ characterization and molecular modeling to reveal reactive and reversible wettability mechanisms, providing a unified framework for CO₂ and H₂ storage systems.

The underground storage of gases, such as CO₂ and H₂, in the porous media is a critical component for achieving carbon neutrality and economical energy storage. While previous research has predominantly focused on gas injection in one piece of uniform porous media, and gravity is often neglected, the reality is that natural storage formations are typically multi-layered porous systems. An in-situ gas injection apparatus based on high-resolution micro-CT was utilized to investigate gas injection behaviors and failure patterns in layered porous media systems. The system includes a reservoir layer and a cap layer, where both capillarity and permeability are meticulously controlled. Our findings reveal that all cases experience cycles of a pressure built-up period and a sudden pressure release when a barrier, either capillarity or effective stress, is overcome. Drainage conditions within the layered system significantly impact both the volume of gas trapped and the failure patterns observed. Effective stress analyses show that the key determinants of failure patterns are capillarity, effective stress, and excess pore fluid pressure, affected by pore size, cap layer thickness, gas injection rate and permeability. Five distinct failure patterns are categorized: capillary invasion, fracture opening, integral uplifting, local heaving, and violent liquefaction-based on two dimensionless parameters. This work provides new insights into understanding the gas injection dynamics in layered porous media.