Research on law of hydraulic fracturing crack propagation controlled by multi-preset slots in long drilling of coal seam

Preset slot is an effective control measure to solve the blank zone problem appeared in the coal and rock mass hydraulic fracturing. Taking Tangkou Coal Mine as an example, RFPA software was used to analyze the crack propagation law controlled by the preset slots on the long drilling along the coal seam strata of the working face. The research shows that: all the main hydraulic fractures controlled by the multi-slot fracturing expand in the direction perpendicular to the minimum horizontal principal stress. There are some preset slots that can preferentially induce hydraulic crack propagation. As the density of the pre-slots increases, the length of the unilateral main hydraulic crack decreases and the crack opening angle increases. The length change of the longest unilateral main hydraulic crack roughly conforms to the linear relationship. The average length of the longest unilateral main hydraulic crack is 26.3 m. The average crack opening angle is 11.8°. The stable pressure of the crack propagation is 18.0 MPa. The reasonable slot density is 0.04 m, and the corresponding slot spacing is 25 m. The average pressure relief area of a single hole is 2 537 m2. The permeability of the main fracture area can be increased by 100 to 200 times.