Permeability Prediction of Unconventional Gas Shale: Implications for Hydrogen Geo-Storage

Greenhouse gas (GHG) emissions pose significant challenges to global climate stability and considerably hinder decarbonization goals in the US. Hydrogen, a clean fuel, offers considerable potential and flexibility to address these challenges by functioning as an energy carrier across multiple energy sectors. Underground hydrogen storage (UHS) is promising given the increasing importance of effective hydrogen storage. This study aims to predict the permeability for evaluating the uptake capacity and injectivity for effective UHS. This study introduces a theoretical model to accurately estimate hydrogen permeability in unconventional gas shale formations by considering the coupled flow mechanisms and geomechanical effects during shale-hydrogen interactions. The intermolecular collision-based flow and molecule-pore wall collision-based flow are taken into account in the developed model. Following the modeling work, laboratory measurements were carried out on shale permeability in H2. The shale permeability tests on H2 were conducted by using pulse decay method under constant confining pressure conditions. The change in permeability ratio with pore pressure variations indicates that the permeability is affected at the initial injection phase, but it reaches a constant with continuous gas injection. Limited increment is presented at the initial depletion phase while the uptake capacity can be recovered with continuous H2 withdrawal. The measured permeability results of H2 fit in close agreement with the proposed theoretical model. Accurately predicting the permeability of hydrogen in unconventional gas shale formations is critical for evaluating the effectiveness of targeted gas shale reservoirs. The proposed model provides a theoretical basis that avoids conducting costly field tests and enhances understanding of the uptake capacity and storage injectivity of hydrogen.