Due to the special physical and mechanical properties and gas production mechanism of coal reservoirs, the changes of their physical properties are different from those of conventional reservoirs during the coalbed methane development process, of which the dynamic change in permeability is the most significant. During the development process of coalbed methane, production pressure difference can promote gas desorption, but meanwhile, it brings serious damage on coal permeability. This study simulated this damage caused by increasing the displacement pressure difference. Results indicate that the permeability of Duanshi and Gaohe samples declined about 71 and 63.3%, respectively, after the displacement pressure difference increasing to 2.50 MPa. Moreover, there was a critical value of pressure decline of coal. When the displacement pressure difference was lower than the value, the permeability would not change. Therefore, it would be best to control the production pressure difference lower than the critical value of pressure decline during the development. If exceeded, a reasonable production system to decrease the damage and to promote forming a high and stable production of a gas well should be adopted.

This study divided the oil shale segments and the quality grades; tested the oil content of oil shale samples in different segments; found out the distribution characteristics of the ore bodies in each segment; identified the ore-bearing properties of oil shale ore bodies; summarized the method, the range, and the parameter determination of resource estimation; and the divisional principle of resource blocks. Then the separate-level profiling method was chosen to delineate the oil shale ore bodies over and under the ground, and the profile lines, the bottom contour lines (horizontal lines), the outcrop lines, the synclinal axis, and the boundary line of the mining area were used to constrain the blocks. Finally, the mineable oil shale amount in the study area was calculated. The results show that the amount of low-quality, medium-quality, and high-quality oil shales are 3,482, 2,598, and 1,348 million tons, respectively.