Research on Gas Mass Transfer Mechanism of Shale Micro-Nanopores

Abstract

Shale reservoirs contain abundant micro- and nanopores and act as both source rocks and gas reservoirs, resulting in gas storage and transport behaviors that differ markedly from those in conventional reservoirs. During shale gas production, adsorption and desorption, together with stress-dependent deformation, alter the effective pore geometry, while gas slippage affects transport through the resulting flow channels. In this study, an apparent permeability model is developed within a capillary framework by coupling adsorption-induced deformation, stress-sensitive pore evolution, and the first-order slippage effect. The calculated permeability is compared with published CH4 and He measurements under different confining pressures, and the effects of effective stress and selected model parameters are examined. The calculated curves reproduce the main pressure-dependent permeability trends observed in the published dataset, with the level of agreement varying among the individual gas-confining-pressure series. At a given pore pressure, apparent permeability decreases with increasing effective stress, while the rate of decrease gradually diminishes. The model results further show that temperature, initial pore radius, elastic modulus, and gas properties influence apparent permeability through their effects on pore geometry, adsorption-induced deformation, stress response, and gas rarefaction. These results provide a basis for further investigation of gas transport and apparent-permeability evolution in shale micro- and nanopores.