Nanofluid-assisted enhanced sealing security for efficient geological hydrogen storage in Saudi Arabian basalt

The modification of hydrophobic rock surfaces to the water-wet state via nanofluid treatment has shown promise in enhancing their geological storage capabilities and the efficiency of carbon dioxide (CO 2 ) and hydrogen (H 2 ) containment. Despite this, the specific influence of silica (SiO 2 ) nanoparticles on the interactions between H 2 , brine, and rock within basaltic formations remains underexplored. The present study focuses on the effect of SiO 2 nanoparticles on the wettability of Saudi Arabian basalt (SAB) under downhole conditions (323 K and pressures ranging from 1 to 20 MPa) by using the tilted plate technique to measure the contact angles between H 2 /brine and the rock surfaces. The findings reveal that the SAB's hydrophobicity intensifies in the presence of organic acids, with significant increases in both advancing ( theta a ) and receding ( theta r ) contact angles upon exposure to organic acid at 323 K and 20 MPa. Contrastingly, the application of SiO 2 nanoparticles under these conditions results in a marked shift towards hydrophilicity, with theta a and theta r decreasing substantially, thus indicating an optimal nanoparticle concentration (0.1 wt% SiO 2 ) for effecting the transition from H 2 -wet to water-wet states. This change in wettability aligns with the known pressure-dependent behavior of contact angles. Moreover, the treatment of organically-aged basalt with 0.1 wt% SiO 2 nanofluids at 20 MPa and 323 K enhances the H 2 column height significantly, from -424 m to 4340 m, suggesting a reduced risk of H 2 migration across the caprock and thereby enhancing both the structural/residual trapping and containment security of H 2 within the basaltic formations of Saudi Arabia. This article highlights the crucial role of SiO 2 nanofluids in improving the efficacy of H 2 storage in basalt, offering a new insight towards the optimization of geological storage solutions for hydrogen, a critical component in the transition to a sustainable energy future.