Hydraulic fracturing weakening roof borehole protection technology

In the case of sequential mining with single wing arrangement in coal mine working face, the drilling along the working face is easily affected by the support stress of adjacent working faces, leading to drilling failure. At present, research on borehole protection focuses on enhancing the strength of the borehole itself, without proposing solutions to the fundamental factors that affect borehole stability. In order to solve the above problems, a hydraulic fracturing weakening roof borehole protection technology has been proposed. By using hydraulic fracturing to weaken the roof, the peak mining support stress acting on adjacent coal working faces is reduced, and the transmission of high support stress to the surrounding coal bodies in the bedding boreholes is blocked. The entire process of screening is carried out in the bedding boreholes to ensure that the gas escaping from the coal body can enter the bedding boreholes. Numerical simulation is used to analyze the changes in vertical stress and plastic zone of the coal body around the borehole before and after hydraulic fracturing weakening the roof. The results show that by weakening the roof through hydraulic fracturing, the peak vertical stress of the coal body around the borehole decreases from 21.2 MPa to 9.1 MPa, and the plastic zone range of the coal body decreases from 19 m to 11 m. According to the numerical simulation results, hydraulic fracturing parameters are determined and tested on site. The results show that after using hydraulic fracturing weakening roof borehole protection technology, the average volume fraction of gas extraction from boreholes increases from 3.6% to 14.1%. The average mixed flow rate of gas extraction decreases from 1.28 m³/min to 0.464 m³/min. There is no occurrence of coal oxidation and CO production in a large area of bedding boreholes. Therefore, hydraulic fracturing weakening roof borehole protection technology can effectively avoid drilling failure and gas leakage, improve drilling and extraction efficiency, and ensure drilling and extraction safety.