New Model of Permeability of Tight Shale Gas Rock Based on Open-System Geomechanics

Finding an adequate description of permeability in shale gas is a challenging problem because of complexity of the rock which contains both organic and non-organic components. Due to small pore size, which is comparable with the mean free path of molecular motion, matrix permeability should include Knudsen and slip flow components as well as conventional Poiseuille one. If we assume as usual that permeability is a function of porosity, k(), then stress and pore pressure dependence of variation of permeability can be found as determined by porosity related effective (Terzaghi) stress, i.e. difference between confining stress and pore pressure (Carroll, 1980; Charlez, 1997):