Experimental study on mapping mechanism of loading process of rock and coal and gas permeability

The research focuses on the mapping mechanism of load process of rock and coal and gas permeability. An experimental system was developed to test the permeability of raw coal samples under different gas pressures and pressure differences. The system can continuously implement constrained annular strain and axial loading. The coal samples were tested under constrained annular strain conditions and then adding axial pressure. The results show that, under constrained annular strain, the permeability decreases gradually with the increase of gas adsorbed by coal and rock, proportional to a power function, which agrees with the previous research results. The results also indicate that the addition of axial stress reduces the permeability by nearly one order of magnitude. The negative effect of stress on the permeability of coal and rock is stronger than the positive effect of adsorption. Furthermore, a gas flow model for the whole loading of coal and rock was established, in which the gas flow in coal was divided into three stages according to the loadings. The gas flow model of coal and rock has physical significance, which represents the migration of coal and rock under different loadings commendably and describes the composition of seepage resistance clearly.