Influence of alumina nanofluids on wettability and capillary sealing of organic-aged shale substrates for H₂ geological storage

The increasing concentration of carbon dioxide in the atmosphere, primarily driven by the combustion of fossil fuels, poses serious risks to global climate stability and public health. As a cleaner alternative, hydrogen (H₂) offers promising potential; however, its widespread adoption is hindered by challenges related to its low density, high reactivity, and safe storage, especially under subsurface conditions. Shale formations are crucial for retaining H₂ underground for geological hydrogen storage. A critical factor influencing this storage potential is wettability, which directly affects H₂ trapping efficiency. Organic contaminants, such as stearic acid, can degrade caprock sealing capacity, whereas nanofluids may offer a solution to mitigate this effect. This study investigates the influence of alumina (Al₂O₃) nanofluids on the wettability of stearic acid-contaminated shale samples under simulated reservoir conditions. Shale cores from the Eagle Ford, Marcellus, and Barnett formations were artificially aged with stearic acid (10⁻² mol/L) to replicate subsurface contamination. Wettability was assessed using the sessile drop method by measuring the brine advancing and receding contact angles on pure, organic-aged, and nanofluid-aged (at Al₂O₃ nanofluid concentrations of 0.05, 0.1, 0.25, and 0.75 wt%) substrates, across a pressure range of 01–16 MPa at a fixed temperature of 323 K. Various characterization techniques were employed to monitor mineralogical and morphological changes. The results indicate that stearic acid and elevated pressure promoted H₂-wet conditions, increasing the brine contact angle and reducing the H₂ column height, which implies decreased capillary trapping. Treatment with Al₂O₃ nanofluids, particularly at 0.25 wt%, reversed the wettability to an intermediate state, increasing the H₂ column height and capillary trapping. These findings underscore the potential of nanofluid-based wettability alteration to enhance H₂ storage security in shale formations, contributing to a broader transition toward sustainable energy systems.