Distribution Patterns of the Dominant Mining Fracture Fields in Pressure Relief Methane Migration

The evolution and distribution laws of fracture fields directly affect the efficiency of mining methane extraction. In this study, a physical model test method and a DIC speckle analysis system were used to examine the distribution laws of the dominant mining fracture fields of pressure relief methane migration in working face advancement processes. The results revealed that during the advancement of working faces, the fracture angles on both sides of the goafs and the top separation fractures form ladder-type overburden fracture structures. A large number of penetrating cracks were generated in the caving zone, transition zone and vertical fracture zone in the ladder structure, which provided dominant channels for methane migration. The average extraction purity of 12 m 3 /min and the average concentration of methane extraction in surface wells were both above 90% in the fracture-filled area. Methane had an excellent migration channel and storage space. As the fracture begins to close, the methane extraction efficiency decreases until the methane extraction concentration was reduced to a minimum of 8.1% and the methane extraction purity was reduced to a minimum of 0.03 m 3 /min. The field data change results of methane extraction were consistent with the experimental theory. The research results can provide references for improving the efficiency of methane extraction and optimizing the layout of drilling wells and their horizons. Highlights The fracture law of mining overburden was studied, and the displacement characteristics of mining overburden were analyzed by DIC system. The distribution characteristics of abutment stress of overlying strata from open-off cut to stop line were studied. The number and angle of cracks in the fracture zone were studied. The extraction parameters of surface wells in a mine were measured on site, and the test conclusions were verified.