Enhancing Hydrogen Storage Efficiency in Organic-Rich Shales Using Silica Nanofluids: A Comprehensive Study on Wettability Alteration

Abstract

Underground hydrogen storage (UHS) is an essential method for advancing a hydrogen (H₂)-based economy by enabling safe storage of H₂ in geological formations. Shale formations serve as an appropriate storage medium due to their extensive availability and restricted permeability, both of which are critical for effective hydrogen sequestration. Nevertheless, the presence of organic matter in shale caprocks frequently reduces their sealing efficiency by altering their wettability from predominantly water-wet to H₂-wet, thereby undermining containment. The use of silica (SiO₂) nanofluid as a wettability modifier has been suggested in order to mitigate this difficulty by restoring water-wet conditions and improving the interfacial tension (IFT). This study examines the effects of treatment with various concentrations of silica nanofluid (SiO₂; 0.05–1.0 wt %) to enhance the sealing performance of high total organic carbon (TOC) Jordanian shale samples under actual geological settings (0.5–1600 psi, 323 K) utilizing brine (1 wt % KCl + 2 wt % NaCl). The wettability is evaluated by using the tilted plate method, and the H₂/brine and H₂/shale interfacial tension (IFT) values are determined before and after the treatment. The untreated shale samples exhibit weak water-wet to H₂-wet conditions, signifying inadequate sealing properties. The application of silica nanofluid considerably enhances the wettability, transforming to a pronounced water-wet condition. In the sample with the greatest TOC, the receding contact angle decreases from 82 to 29° with the application of 0.4 wt % SiO₂. In the sample with the lowest TOC, however, only 0.1 wt % SiO₂ is needed to alter the contact angle from 76 to 38° under the same conditions. As the pressure increases, the IFT value of the shale/H₂ system tends to decrease, although a slight increase is observed with relatively high concentrations of silica nanoparticles, thus, suggesting a mechanical barrier effect. This study is the first to investigate the effects of silica nanofluids on actual organic-rich shales, providing a genuine assessment of their application. The results demonstrate the effectiveness of silica nanofluids in improving wettability and sealing efficiency, thus providing a feasible alternative for secure and efficient UHS.