Meikuang Anquan (May 2022)
Technology and application of sublevel sand fracturing and permeability enhancement of coal seam roof in underground coal mine
Abstract
In order to solve the problems of hydraulic fracturing fractures easy to close, uneven fracturing, poor fracturing effect and difficult gas drainage in broken soft coal seam, combinning with the current mature drilling technology, self-developed directional sand blasting perforation equipment and process technology, hydraulic sand fracturing equipment and process technology, the idea of “directional sand blasting perforation + staged sand fracturing” for directional long drilling of coal seam roof to increase coal seam permeability was proposed, and the engineering test has been carried out in Xinjing Coal Mine 3# coal seam roof in Yangquan Mining Area. The hydraulic sand fracturing technology of long directional drilling in coal seam roof is formed. The test results show that the long drilling hole in the roof of 609 m coal seam is divided into 6 sections for sand fracturing, the construction displacement is more than 1 m3/min, the single section liquid injection is more than 150 m3, and the cumulative liquid injection is 967 m3; the fracture pressure from the hole bottom to the orifice decreases gradually, and the maximum fracture pressure is 29.6 MPa. The highest proportion of walnut shell sand injected is 3%, the maximum injection of walnut shell sand in a single section is 2.41 t, and the cumulative addition is 13.11 t. Statistical analysis of 60 d gas drainage data shows that the average gas drainage concentration is 60.6%; the maximum net amount of gas drainage in a single day reaches 1 381.5 m3. The gas drainage concentration is 8.81 times and 3.96 times higher than that of bedding hole and kilometer hole respectively; the net extraction volume of 100 m borehole was increased by 21.4 times and 7.28 times respectively, and a good antireflection effect was obtained.
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