Adsorption-desorption gas relative permeability through mesoporous media - network modelling and percolation theory

Gas relative permeability in mesoporous media is investigated during both adsorption and desorption of a condensable vapour which causes pore blocking in the structure of the porous network. Three-dimensional regular lattices of various pore connectivities are considered and compared to effective medium (EMA) models and Bethe trees of infinite size. During adsorption, the corresponding relative permeability curves exhibit a nearly quadratic behaviour with the volume of adsorbate, in full agreement with percolation theory, while EMA predicts a linear relation between these properties. Bethe trees give a very good approximation of the relative permeability curve of three-dimensional regular networks, provided that the connectivity of the Bethe tree is properly adjusted so that the same percolation threshold is obtained with corresponding regular network. During desorption, relative permeability is only a function of accessible pores. However, the trapped supercritical pores contribute to vapour occupancy during adsorption and not during desorption resulting in hysteresis loops in the corresponding volume of adsorbate. In the case of gas relative permeability experiments using different sets of mesoporous materials and adsorbates, when reduced relative permeability curves are considered in the vicinity of the percolation threshold, they all exhibit a universal behaviour regardless the topology of the porous medium and the nature of the adsorbate. (C) 1998 Elsevier Science Ltd. All rights reserved.