Experimental study on permeability and effective porosity of anisotropic layered phyllite

The experiments on gas permeability and effective porosity of layered phyllite specimens are conducted by using a rock automatic triaxial servo and gas permeability panel. Two stress paths of conventional triaxial compression and confining pressure cyclic loading and unloading are set up in the experiments. The evolution rules of gas permeability and effective porosity with bedding dip angle and deviatoric stress are studied, respectively. The results show that under the same confining pressure, the initial gas permeability k₀ changes in a "W" shape with the increase of the bedding angle β, and reaches the maximum value at β=45°. During the confining pressure cyclic loading-unloading process, the gas permeability decreases with the loading of the confining pressure, then increases while unloading. The gas permeability detected during unloading is smaller than that during loading. An exponential relationship is observed between the effective porosity and the gas permeability of the layered phyllite. The gas permeability parallel to the bedding direction is much greater than that perpendicular to the bedding direction. The variation of the effective porosity and gas permeability with deviatoric stress undergoes initial consolidation stage linear elastic stage, and plastic deformation stage. With the increase of the deviatoric stress, the effective porosity and gas permeability of rock specimens decrease first, then keep stable, and finally increase rapidly, and reach the maximum when the slope of stress-strain curve is close to zero.