Stress-dependent permeability of two-solid constituent model of gas shales 页岩气两固体成分模型的应力相关渗透率
Because gas shales consist of organic and inorganic solid components, the stress and pore pressure dependence of permeability of shale gas rock is considered in the model of porous medium with two solid constituents. It is done in the framework of a generalized model of composite sphere phases each of them being gas/fluid saturated. It is shown that the total mean stress in each of the phases is different from the confining stress even for a homogeneous state. This leads to a more complicated
... more complicated dependence of permeability rather than that of Terzaghi effective stress, i.e. confining stress minus pore pressure as in the case of a one-solid constituent porous medium. Additional dependence of permeability on pore pressure is captured by considering Knudsen and slip flow contributions. Because depletion-induced variation of pore pressure leads to the variation of eigen-strain, the resultant strain and stress exerted at the reservoir by surrounding country rock is found by using Eshelby-type inclusion model. The depletion-induced evolution of reservoir permeability is expressed as a function of pore pressure. The model provides recommendation for maximum drawdown which still allows preventing collapse of porosity and permeability of softer organic constituent.