Key technologies for extraction and identification of gas target area for pressure relief in inclined thick coal seam

In order to study the dip angle effect on the evolution law of the target area for pressure relief gas drainage in inclined thick coal seams, the physical similarity simulation test and theoretical analysis were combined to study the fracture evolution in the target area under different coal seam dip angles. The evolution law of broken fracture’s width, the area proportion of bed-separated fracture, and the fractal dimension of fracture with the change of coal seam dip angle in the target area were obtained, and then the coal seam dip angle effect model of the targeted area evolution was established. The results showed that the broken fracture’s width presented the distribution characteristics that the boundary area on both sides of the goaf was greater than that in the middle, and the low horizon was greater than that in the higher horizon. What’s more, the broken fracture’s width was strongly affected by the hinged beam. With the increase of the coal seam dip angle (0° < 15° < 30°), the broken fracture’s width in the upper region of the first layer of hinged beam is significantly reduced compared with that in the lower region, which is only 52.8%, 64.3%, and 71.1%, respectively. The area proportion of bed-separated fracture in the dominant gas migration channel zone was the largest at the bottom, followed by the top, and the smallest in the middle. The fractal dimension of overlying fractures decreased first and then increased as a whole. The fracture evolution laws were obviously different on both sides of the layer where the hinged beam of the first layer and the minimum fractal dimension of the fracture were located. Therefore, the dominant channel belt of gas migration was divided into low-layer target areas, middle-layer target areas, and high-layer target areas according to the level of the spatial horizon. Finally, based on the theory of mining fracture ellipse belts and the dominant gas migration channel zone at the working face side, the mathematical equation of the target area in inclined thick coal seams was established considering the coal seam dip angle, and the basis for selection of pressure relief gas drainage methods in the targeted area was formed. It provided a reference for optimizing the parameters of pressure relief gas drainage in an inclined, thick coal seam working face.