Research on evaluation system of hydraulic fracturing for directional long drilling of double thick combined hard roof

Aiming at the problem of strong mine pressure in the mining process of thick coal seam working face with double thick combined hard roof, this paper proposes a directional long drilling hydraulic fracturing scheme, and based on the pressure measurement, transient electromagnetic and borehole peeping method, the visual monitoring and evaluation of directional long drilling hydraulic fracturing crack propagation is carried out from four aspects : inside and outside the hole, dynamic and static. The research results show that the fracturing process includes the development and expansion of microcracks around the borehole, the emergence of macrocracks, the development of microcracks around macrocracks, and the emergence of new macrocracks until the completion of fracturing. The resistivity of the rock layer is low within the range of 20 m in the radial direction of the borehole, and the large cracks are more developed; the influence range of the three designed boreholes after fracturing can basically cover the whole roof control area. The fractures of each fracturing section in the long borehole can be connected, and the longitudinal and transverse fractures in the borehole develop alternately to form a three-dimensional fracture network. After fracturing, the total energy and total number of roof microseismic events are significantly reduced, and the roof energy of the fractured horizon is released in advance, showing “high frequency and low energy”, and the pressure intensity of the working face is obviously improved.