Abstract
To solve the problems of gas predrainage in deep seams with “three softs” and low-air permeability, hydraulic punching pressure relief antireflection technology is proposed on the basis of the research background of gas predrainage technology in Lugou Mine to alleviate technical problems, such as low gas drainage efficiency, in this mine. Through the analysis of the mechanism of hydraulic punching and coal breaking, combined with FLAC3D software, a hydraulic punching pressure relief antireflection model is established. Then, the fracture radii of coal rock are simulated and calculated. The results show that, under hydraulic punching with a water pressure of 10 MPa and coal outputs of 3 m3, 6 m3, 9 m3, and 12 m3, the fracture radii of coal and rock are 3.4 m, 4.8 m, 5.5 m, and 5.9 m, respectively. Using the software to fit the relationship between coal output V and hydraulic punching fracture radius R under the same water pressure, R = 2.32479 V0.3839 is obtained. The field test is carried out in the bottom drainage roadway of 32141 in Lugou Mine. The application effect is as follows: the gas concentration of hydraulic punching with a coal output of 3 m3 is twice that of ordinary drilling, and the coal output of hydraulic punching with a coal output of 6 m3 is four times that of ordinary drilling. The extraction concentration is four times that of ordinary drilling, and the extraction concentration of hydraulic punching with a coal output of 9 m3 is 6.4 times that of ordinary drilling. Combining the results of the numerical simulation and taking into account the actual construction situation on site, the coal output of water jetting from the borehole is 9 m3, and the fracture radius is 5.5 m. This outcome means that the effective half radius is 5.5 m, and the borehole spacing is 7.7 m. These values are the construction parameters for large-scale applications. This proposal provides effective technology and equipment for gas drainage in the deep three-soft coal seam. Consequently, it has promotion and reference significance for gas drainage in coal seam of the same geological type.
Highlights
Coal is a basic energy source in China, and it is an important raw material. e coal industry is an important basic industry that is related to the country’s economic lifeline and energy security
In China’s primary energy structure, coal is expected to be the main energy source for a long time, which will continue to increase China’s coal output [1]. e high coal output has led to the continuous increase in the intensity of coal mining and the continuous increase in mining depth
On-site measurement and research have shown that deep mining is not defined by the mining depth and by the depth of mutation of nonlinear physical and mechanical phenomena in the engineering rock mass and the depth space below it as the mining depth increases
Summary
Coal is a basic energy source in China, and it is an important raw material. e coal industry is an important basic industry that is related to the country’s economic lifeline and energy security. Erefore, given the characteristics of the deep stress environment, an urgent need has emerged among the majority of scientific and technological workers to study the mechanism of pressure relief and reflection improvement of the “three-soft” outburst coal seam and to provide a theoretical basis for the prediction and forecast of accidents. The drilling imaging results reflect the shape of hydraulic punching holes and the position and shape of the cracks caused by hydraulic punching pressure relief; they provide a theoretical basis for the analysis of the hydraulic punching pressure relief mechanism and the law of gas migration after hydraulic punching [24] He et al established an elastoplastic model of coal around hydraulic punching considering the plastic softening and expansion characteristics of coal; they analyzed the effect of pressure relief and reflection improvement of hydraulic punching and the variation law of the pore diameter; they formulated the technology of preventing borehole blockage and gas injection displacement [25]. Dense, and hard. e karst fissures are well developed. ey are rich in water and contain a lot of calcite veins and pyrite crystals
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