Adsorption-Induced Deformation in Microporous Kerogen by Hydrogen and Methane: Implications for Underground Hydrogen Storage

Accurately assessing
the adsorption and diffusion behaviors of
H2, CH4, and their mixtures are essential for
estimating underground hydrogen storage (UHS). This understanding
is critical for the safe and efficient storage of H2 in
depleted shale gas reservoirs. Although H2 adsorption in
kerogen has been extensively studied, adsorption-induced swelling
remains unexplored in UHS. In this study, we investigate adsorption
mechanisms using Lagrangian and Eulerian approaches and analyze diffusion
in kerogen through molecular simulations. Our results reveal that
in the presence of cushion gases like CH4, which exhibit
stronger adsorption than H2, neglecting kerogen deformation
can lead to an underestimation of storage capacity by approximately
40%. Furthermore, increasing pressure makes H2 adsorption
behavior deviate from the consistent swelling trend that is observed
with CH4, with kerogen either swelling or contracting depending
on the pore size. Simulations also predict that H2 self-diffusion
coefficient in porous kerogen is 1 order of magnitude higher than
CH4. These findings highlight the importance of incorporating
kerogen flexibility into the modeling of UHS involving multiple gas
species to improve the accuracy and safety of H2 storage
operations in shale reservoirs.