ADSORPTION-DESORPTION GAS RELATIVE PERMEABILITY THROUGH MESOPOROUS MEDIA - NETWORK MODELING AND PERCOLATION THEORY

Gas relative permeability in mesoporous media is investigated during b oth adsorption and desorption of a condensable vapour which causes por e blocking in the structure of the porous network. Three-dimensional r egular lattices of various pore connectivities are considered and comp ared to effective medium (EMA) models and Bethe trees of infinite size . During adsorption, the corresponding relative permeability curves ex hibit a nearly quadratic behaviour with the volume of adsorbate, in fu ll agreement with percolation theory, while EMA predicts a linear rela tion between these properties. Bethe trees give a very good approximat ion of the relative permeability curve of three-dimensional regular ne tworks, provided that the connectivity of the Bethe tree is properly a djusted so that the same percolation threshold is obtained with corres ponding regular network. During desorption, relative permeability is o nly 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 usi ng different sets of mesoporous materials and adsorbates, when reduced relative permeability curves are considered in the vicinity of the pe rcolation 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.