Directional three-dimensional hydraulic fracturing technology and its application of super-long borehole in hard and thick roof of extra-thick gently inclined coal seam

In view of the large area hanging roof caused by the mining of extra-thick coal seam under the condition of hard and thick roof in Xinjiang, the phenomenon of strong mine pressure may be induced. Taking the I010206 working face of Kuangou Coal Mine as an example, analyzes the roof caving form of extra-thick gently inclined coal seam and the control idea of strong mine pressure of hard thick roof by theoretical analysis, numerical simulation, field monitoring and engineering test, defines the reasonable fracturing parameters, puts forward the ultra-long borehole directional three-dimensional hydraulic fracturing technology and carries out the field test. The results show that the pore water pressure decreases rapidly within 5 m with the increase of the radial distance from the borehole. When the distance between the fracturing sections is small, the influence of the two fracture propagation is easy to cause the fracture deflection. When the water injection rate increases from 20 m³ to 35 m³, the crack propagation length increases by 50%. Considering the strength of the fracturing layer, the range of crack interaction and the fracturing effect, the optimal parameters of hydraulic fracturing in Kuangou Coal Mine are determined as follows: the initiation pressure is 17 MPa, the borehole spacing is 50-72 m, the fracturing section spacing is 30 m, and the single section water injection is 35 m³. Based on the geological conditions of Kuangou Coal Mine, the directional staged hydraulic fracturing technology and process of double-thick combined rock strata with double-seal single-card multi-point dragging are proposed. After fracturing, the number of microseismic events of hard roof is greatly reduced, and the peak pressure of roof is effectively reduced. The research in this paper can provide a solution to the phenomenon of strong ground pressure in the mining of hard thick roof in similar conditions.