Influence of the spatial position of horizontal well in roof strata of crushed soft coal seam on the propagation of fracturing fractures

The staged fracturing technology of horizontal wells in the coal roof is a new method for the development of coalbed methane in the development area of soft，low⁃permeability coal seams. In order to explore the influence law of horizontal well spatial position on fractured fracture propagation，based on the related theories of elasticity and frac⁃ ture mechanics，a fracture propagation stress analysis model considering formation dip angle and wellbore trajectory is established. The crack propagation process and influencing factors were theoretically analyzed. The critical water pres⁃ sure for crack initiation，diversion and interlayer propagation is deduced. The numerical simulation is used to reveal the influence law of horizontal wellbore spatial position on fracture propagation. Results show that:1 the relative position of horizontal wellbore and coal seam space affects the expansion and shape of fractured fractures. It is mainly affected by factors such as vertical stress，horizontal stress of roof rock layer，horizontal stress of coal seam，perforation angle， perforation depth，formation dip angle，distance between wellbore and coal，coal⁃rock interface properties，roof rock and coal⁃rock mechanical properties. 2 The smaller the angle between the perforation hole and the formation，the lar⁃ ger the fracture turning angle and turning distance，the higher the fracture initiation pressure. Also，the crack height is not easy to control，the length of the crack extending to the upper part of the roof is large. The closer the wellbore is to the coal seam，the more favorable it is for the fracture to propagate through the layer，and the farther the distance is，the higher the fracture propagation pressure. The longer the perforation hole length，the lower the fracture initiation pressure. The longer the perforation hole length， the lower the fracture initiation pressure. When the dip angle of the coal seam increases to 45°，the fractures mainly expand in the roof of the coal seam，and the fracture extension pressure fluctuates greatly and the extension pressure is high. 3 The perforation position of a horizontal well is opti⁃ mized through the research results. The field application results show that the research results are useful to the pro⁃ motion and application of the staged fracturing coalbed methane drainage mode of coal roof horizontal well.