Experimental Comparison Study on Permeability of Coal and Shale

The seepage laws of coal and shale were studied by means of the conventional triaxial seepage simulation test. The experimental results showed that the permeability of shale sample is three orders of magnitude lower than that of coal sample. In order to compare the two, we introduce the permeability change ratio I, so that the difference between the two can be shown in the same picture. Based on these results, we suggested that the permeability of coal and shale has the same trend, the permeability variation of the two samples matches with the deformation characteristics of the rock and there is a minimum permeability point between the elastic phase and the plastic expansion phase, the permeability decreases with the increasing of confining pressure, but the attenuation amplitude and decay rate of coal are both higher than that of shale, and it also increases exponentially with the increase of the pore pressure, on the contrary, shale is more sensitive to gas pressure.