Research and application of “concentric ring” reinforcement and sealing technology for gas drainage boreholes in soft coal seams

The problems of easy-to-stability and difficult sealing of gas drainage boreholes in soft coal seams directly affect the efficient extraction of gas in soft coal seams. After the holes are drilled and retreated in the construction of soft coal seams, the holes in the holes fail to be sealed in time. In addition, a large number of gas leakage channels are formed in the coal crushing area at the orifice, resulting in seal failure, which brings hidden dangers to mine production and a waste of time and economy. This paper starts with the theoretical analysis of the stress on the sealing section of the drill hole, and on the basis of solving the stress on the coal body in the hole breaking area by using the viscoelastic mechanical model, combined with the theory of the external conditions affecting the hole collapse of the hole opening in the soft coal seam, studies the causes of the hole collapse of the hole opening in the soft coal seam and puts forward reasonable solutions. Based on this, the “concentric ring”reinforcement sealing technology is proposed, and it is described in detail from the aspects of the physical model, technical principle and process, Finally, the field application test was carried out in the N2106 soft coal seam working face of a mining area in Shanxi. The results show that under the time effect, the broken area of the hole opening in the soft coal seam is easy to enter the stage of rapid deformation, and its strong adsorption line, easy expansion and other characteristics, coupled with the severe disturbance of the drill pipe to the hole opening after drilling offset, eventually lead to the deformation and collapse of the hole opening after drilling withdrawal; The test boreholes reinforced and sealed with “concentricring” did not collapse after withdrawal. The gas concentration remained above 30% in the first 30 days. The maximum pure gas flow of the boreholes reached 0.053 m3 / min on the 30th day of extraction. Compared with the traditional sealed boreholes, it was found that the sealing effect of “concentric ring” reinforced and sealed boreholes was better than the traditional sealing technology. © 2022 China Coal Society. All Rights Reserved.