Consistent modeling of coupled adsorption and transport in high-pressure nanoconfined gases

Coupled adsorption and non-equilibrium transport of nanoconfined gases at high pressure appears in many applications, such as shale gas extraction, CO 2 geological sequestration, and subsurface H 2 storage. The interplay among adsorption, transport, and spatial variations in density and viscosity poses a significant challenge for predicting macroscopic flow behaviors. In this study, we show that shale gas transport often occurs in a regime where non-continuum, dense gas, and confinement effects intersect, rendering dilute-gas kinetic theories and continuum-based approaches inadequate. To address this, we employ a confined kinetic model to account for gas–surface interactions governing gas adsorption and molecular interactions responsible for real-gas behaviors at high pressure. This formulation provides a self-consistent treatment of both adsorbed and free gases without requiring ad hoc coupling rule. Adsorption, viscosity inhomogeneity, and transport characteristics are systematically examined across pressure, wettability, and confinement conditions, with molecular dynamics simulations used as benchmarks. These results demonstrate that high-pressure nanoconfined flows lie beyond the scope of traditional continuum and Boltzmann models, highlighting the need to consistently account for both adsorbed and free gases in nanoconfined flow systems.