Gong-kuang zidonghua (Nov 2021)
Test of roof interception directional drilling for close distance coal seam group gas control in Qidong Coal Mine
Abstract
In the existing methods of close distance coal seam group gas control, there are problems such as large engineering quantities, high cost and long cycle. In order to solve the above problems, taking the 94 mining area of Qidong Coal Mine as the research object, a gas control method by using roof interception directional drilling is proposed. Firstly, the roof interception directional drilling with multiple upward branch holes is constructed in the roof of the mining coal seam. Secondly, the upward branch holes are used to extract the gas from the upper adjacent coal seam in advance. Finally, the main hole is used to extract the pressure relief gas from the upper adjacent seam and the gas from the working face of the mining coal seam and the goaf during the coal seam mining. This method improves the gas extraction effect of the close coal seam group from 2 aspects of pre-extraction and mining pressure relief extraction, and solves the problems of gas occurrence parameter measurement, directional drilling and hole protection of complex fractured formation. In order to solve the problems of the design and construction of roof interception directional drilling, the method adopts directional drilling for coal seam exploration and pressure maintaining sealed coring technology, composite directional drilling and composite slag removal technology, and steel screen pipe completion technology to realize efficient hole formation of roof interception directional drilling for close coal seam group and long-distance accurate gas measurement. Field tests are carried out in the 94 mining area of Qidong Coal Mine. One roof interception directional drilling is completed, the main hole depth is 608 m, the construction branch holes are 6, the gas content is tested by sealed coring technology twice, and the lower protective screen pipe is 485 m. The gas extraction test is carried out for 207 days. The initial gas extraction net amount is 0.35 m3/min. After 30 days of extraction, gas extraction net amount gradually drops to below 0.1 m3/min. After 65 days of extraction, the overall gas extraction net amount remains stable. The test results show that the roof interception directional drilling can pre-extract the adjacent coal seam gas effectively, reduce the coal seam gas content in advance, and reduce the pressure relief gas emission from the source during the later mining of the working face.
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