Gas permeability through swelling porous media: Insights from coarse-grained pore-scale simulations

Abstract

Sorption-induced swelling can decrease porosity and permeability of the porous medium, affecting the long-term injectivity in rock matrix during CO2 geologic storage. This study employs an innovative coarse-grained model to integrate fluid flow with solid deformation at the pore-scale, exploring gas permeability within swelling nanoporous media. The nanoporous media are composed of spherical pores between 35.4 nm and 106.2 nm to represent pore networks embedded within organic matter. Gas transport is initiated by creating a pressure gradient between two gas reservoirs placed at the two sides of the nanoporous structure. The results indicate that solid swelling (~40%) can significantly decrease permeability (up to 100%). Gas permeability curves demonstrate a linear decline with the increasing gas-solid interaction energy in both swelling and non-swelling porous media, with solid swelling exerting a greater influence on permeability. Surprisingly, in the regime of weak gas-solid interactions, the porosity and permeability of flexible porous media increase, possibly caused by gas flow-induced pore throat opening. It is found that nanoporous media with lower initial porosity experience a greater permeability decline during swelling. The relationship between permeability and porosity changes shows a linear increase characterized by different slopes with varying initial porosities, whilst it is also impacted by pore size distributions. These findings provide valuable insights into the complex interactions among gas transport, solid deformation, and porosity changes in nanoporous media, with implications for understanding and optimizing gas production and storage in realistic geological environments.