Broken soft coal seam is widely distributed in China, which has the characteristics of broken soft, poor air permeability and difficult pore formation. It is more difficult to control gas, which restricts the sustainable and healthy development of mine. In order to further explore the new ideas of gas treatment in crushed soft outburst coal seam, CCTEG Xi'an Research Institute (Group) Co., Ltd., proposed for the first time a new model of advanced gas intensive extraction in the segmented fracturing area of directional long borehole near the roof of crushed soft outburst coal seam, and developed hydraulic sand blasting continuous prefabricated guide fracture and sand fracturing equipment in the hole. The technology of hydraulic sandblasting continuous prefabrication of guide fractures and hydraulic sand-adding stage fracturing in open hole long borehole roof of underground coal mine is pioneered, forming a comprehensive evaluation method integrating geophysical and geochemical exploration.
The technology achievement completed the field industrial test of 2 holes in the underground mine of Xinjing Coal mine in Yangquan, and the length of directional hole of coal seam roof reached 609m. Directional sandblasting prefabricated guide cracks 50 times, sand ratio 3%, the cumulative use of quartz sand 19.8t; In 10 stages of single-hole fracturing, the injection volume of single stage is 166-235m3, sand ratio is 2.02%~2.56%, the accumulative injection of fracturing fluid is 1845m3, walnut shell sand 23.36t, KCL17.2t; The fracturing influence radius is 50~70m, the average gas mixed flow rate is 8.56m3/min, the average methane pure amount is 2810.6m3/d, and remarkable economic and social benefits have been achieved.
The research results have broken the inherent mode of pre-pumping gas in soft and low-permeability coal seams, filled the blank of hydraulic sand subsection fracturing technology in underground coal mines in China, improved the anti-reflection technology system of hydraulic fracturing in underground coal mines, realized the goal of advanced gas efficient pre-pumping in large areas of coal seams in underground coal mines, and provided a technical reference for the comprehensive prevention and control of gas in coal mines with similar geological conditions in China.
