Snap-Off Effects and High Hydrogen Residual Trapping: Implications for Underground Hydrogen Storage in Sandstone Aquifer

Hydrogen (H₂) is a promising clean fuel that could replace fossil fuels for the actualization of the net zero carbon energy transition. Underground hydrogen storage (UHS) in sandstone formations is an essential component of the hydrogen economy value chain for achieving large-scale H₂ storage. In this study, snap-off effects and impacts of high hydrogen residual trapping on the viability of UHS in a Gosford sandstone formation were assessed from initial and residual H₂ saturations in the miniature core plugs. The flooded cores were imaged with X-ray microcomputed tomography (μCT) to identify the fluid (brine and H₂) distributions in the pore spaces. Results showed the presence of large interconnected stable H₂ clusters after the drainage process, with an initial H₂ saturation of almost 53%, suggesting that hydrogen will occupy more than half of the pore volume during storage. However, several disconnected H₂ ganglia and the snapped-off of H₂ droplets from the pore throats were noticed after the imbibition stage with almost 44% residual H₂ saturations. Such highly residually trapped H₂ in the strongly water-wet Gosford sandstone will be difficult to mobilize, resulting in the possible withdrawal of just 9% stored H₂. The study suggests that the water-wet system could produce high H₂ residual saturations, which is unfavorable for hydrogen withdrawal and extraction at the peak energy demand period due to disconnection and trapping of the nonwetting phase.