Research on the Development of Hydraulic Flushing Caverning Technology and Equipment for Gas Extraction in Soft and Low Permeability Tectonic Coal Seams in China

[Image: see text] Soft and low permeability tectonic coal seams (SLPTCSs) are widely distributed in China. In SLPTCSs, because of the difficulty of gas extraction, coal and gas outburst accidents occur frequently. In this paper, with the principle of stress unloading and permeability enhancement in SLPTCSs analyzed, it is put forward that the key technology to realize stress unloading and permeability enhancement in SLPTCSs is caverning by hydraulic flushing. In addition, the development of hydraulic flushing caverning technology and equipment in China is also further systematically studied. Field tests on the application of highly integrated equipment for caverning by hydraulic flushing have been carried out in the Shijiazhuang coal mine and Pingdingshan no. 8 coal mine. The results show that the widely used drilling and hydraulic flushing packaged equipment and drilling and mechanical cutting packaged equipment for caverning in coal seams can efficiently enlarge caverns in SLPTCSs, reduce the amount of workload for hole-drilling in the coal seam, improve the permeability of the coal seam by 23.9 times, and increase the concentration and pure volume of gas extracted in boreholes by more than two times. Highly integrated hydraulic flushing caverning equipment can realize high-efficiency stress unloading and permeability enhancement of the coal seam, which provides beneficial guidance for gas control of SLPTCSs.