Study on combined extraction technology of underground longborehole and CBM ground-well fracturing

Due to the high gas content and low permeability of coal seam in Jincheng mining area,the single ground or underground gas drainage effect is not ideal.In order to make the coal mining safe,a continuous exploration that combined ground fracturing with underground long holes gas drainage to increase permeability become more and more important.The fracture morphology and effective radius of the test well fracturing were evaluated by artificial seismic monitoring techniques such as microseismic method and potential method.The parameters such as gas flow and gas concentration in the test area were investigated,and the temporal-spatial relationship between ground fracturing and underground gas extraction were analyzed.The results show that the fracturing range of the ground well in the test area was elliptical,with the long semi-axis being 120～150 m and the short semi-axis being 50～80 m,and most of the crack form was horizontal.The gas flow rateof 100-meter borehole in the affected zone is 1.33～17.50 times outside the fracturing zone,and the gas concentration increased by an ave rage of 35%.The closer the ground fracturing is combined with the downhole drainage,the better the drainage effect is.The coal seam with better construction stability after ground fracturing construction is preferred.After the fracturing crack and the coal body reach a new dynamic balance,and then drilling the coal seam.After comprehensively considering the drainage effect and the safety of the well,that the distance between the bottom of the fractured well and the excavated roadway and the constructed drilling hole distance of 150～200 m is suitable.