Gas Extraction Mechanism and Effect of Ultra-High-Pressure Hydraulic Slotting Technology: a Case Study in Renlou Coal Mine

Ultra-high-pressure hydraulic slotting technology is an effective method to realize pressure relief and permeability enhancement of a single coal seam. In this paper, through a hydraulic slotting borehole-based total gas extraction amount calculation model, it was concluded that ultra-high-pressure hydraulic slotting technology could increase the gas extraction surface area, improve the gas flow mechanism, and transform single-layer radial flow into interlayer, radial composite flow, thus greatly enhancing the gas extraction efficiency. Based on theoretical results, a field test was conducted in the Renlou coal mine, Anhui Province, China. According to the actual characteristics of the 7 2 coal seam in the Renlou coal mine, the key slotting parameters of this coal seam were determined. The gas extraction sources of each coal seam could be determined accurately through multi-gas source identification and tracer technology, and the effect of hydraulic slotting pressure relief and permeability enhancement was investigated. The test results indicated that the 100-day gas extraction concentration in boreholes using ultra-high-pressure hydraulic slotting technology was 2.68–7.59 times that in conventional boreholes. The average daily pure extraction volume of slotting boreholes was 3.94 times that of conventional boreholes. Based on the calculation of the gas extraction radius of boreholes in the slotted area, it was found that, under the condition of meeting the same control range of outburst elimination, drilling work could be reduced by more than two-thirds. These achievements could provide critical references for the application of ultra-high-pressure hydraulic slotting technology.