Study on fracture compression and permeability of water-bearing coal

In order to study the influence of the water content, the effective stress and the fracture compressibility on the permeability of coal during deep coal mining, isothermal adsorption test and seepage test of coal under different water content conditions were respectively performed by using HCA-type high-pressure capacity method adsorption device and gas-containing coal thermal-fluid-solid triaxial servo seepage device. A coal permeability model considering the combined effect of the water content and the fracture compressibility was established, and the change law of the effective compressibility coefficient and the permeability of coal under different water content conditions was analyzed. The results show that, when the gas pressure is constant at 1 MPa, the axial and radial strains of coal increase with increasing the effective stress, and that, when the effective stress is constant, the axial and radial strains of coal and the gas flow decrease gradually with increasing the water content. As the gas pressure increases, the coal gas adsorption capacity first increases and then tends to be saturated after the gas pressure reaching a certain value between 1 and 2 MPa. Under the same water content, the permeability of coal decreases with increasing the effective stress. When the effective stress is constant, water has a limiting effect on the permeability of coal, in other words, the permeability decreases with increasing the water content. There is a negative correlation between the adsorption deformation and the effective compressibility coefficient at different water cuts, and the effective compressibility coefficient has a negative correlation with the water cut. The calculated permeability by the developed model is basically consistent with the measured, showing that the developed model can better characterize the evolution law of the coal permeability with increasing the effective stress under different water content conditions. © 2020, Science Press. All right reserved.