Coupling of diffusion-dissolution-deformation on the nature of sorption hysteresis in nanoporous shale kerogen

Despite being closely relevant in shale gas production, desorption of CH₄ and CO₂ in deformable shale media remains poorly understood. Sorption hysteresis of CH₄ and CO₂ is experimentally observed in kerogen, and the underlying mechanism needs to be unraveled. Here, we develop a microscopic modeling setup to reasonably reproduce the experimentally observed hysteresis using atom-scale simulations. Various previously suggested mechanisms including capillary condensation, chemical interaction, insufficient equilibrium, and surface heterogeneity, are excluded from the hysteresis origins by detailed sorption studies. The observed hysteresis is governed by diffusive mass transfer of dissolved gas in flexible structure, namely, the coupling of diffusion-dissolution-deformation. The worse-connected porous network and the restricted expulsion of aggregated dissolved molecules upon desorption are discussed as the origins of the coupling protocol. These findings significantly enhance the understanding of hysteresis phenomenon in amorphous materials, which, as well as the proposed microscopic modeling, is widely applicable to other soft nanoporous materials.