作者：Runsheng Lv ，Bing Li, Zhimin Song, and Gaofeng Liu
關(guān)鍵字：Effective stress; Permeability; Deformation; Anthracite
論文來源：期刊
發(fā)表時間：2018年
Coalbed effective permeability is widely used as a primary index to evaluate gas-drainage effect in CBM exploitation field. However, it seems to be difficult to obtain by reason of dynamic change in close relationship with crustal stress, methane pressure, porosity, and adsorption. Due to their dissimilar adsorption properties and tectonic deformation degrees, different types coal containing gas have various stress–strain and gas seepage curves. The paper presents the experimental investigations of the dynamic relationship between coal permeability and deformation under load. In this work, stress–strain and permeability investigations were performed using anthracite lump with a vitrinite re?ectance of about 3.24 % at various pressures and temperatures. The permeability (including the initial, minimum, and maximum) decreased with increasing temperature. At a constant confining pressure, the strains in different directions almost all increased with increasing axial stress and decreased with increasing pore methane pressure during the pre-fracture stage. At a constant pore pressure, the compression strength of the coal specimens increased approximately linearly during the pre-fracture stage and sharply decreased during the post-fracture stage, while the permeability decreased rapidly and then increased slowly pre-fracture and remained stable during the post-fracture stage. The permeability of the coal specimens mainly depended on
the inner fissures. The permeability was greater during the post-fracture than pre-fracture stage. At the same temperature, the gas seepage curve of each coal specimen could be divided into three sections: decreasing, increasing, and constant sections. The necessary time for the permeability to reach a steady state increased as the confining and pore pressures increased. At high confining pressures (i.e., 6 MPa and 8 MPa), no significant differences between the methane seepage velocities of the specimens were evident, and their seepage
curves were similar to pre-fracture. However, clear differences were observable post-fracture. The seepage abilities of the coal specimens were more sensitive to stress than temperature in the same condition.