HAN X M, LIU B Y, XUE L B,et al.Borehole wall instability mechanism of gas drainage in-seam borehole under disturbance of drill pipe drilling[J].Journal of Henan Polytechnic University(Natural Science) ,2023,42(3):18-26.

doi:10.16186/j.cnki.1673-9787.2021100023

Received:2021/10/12

Revised:2022/03/15

Published:2023/05/25

Borehole wall instability mechanism of gas drainage in-seam borehole under disturbance of drill pipe drilling

HAN Xiaoming1,2, LIU Bingyu1,2, XUE Liubing1,2, ZHANG Xiaoming1

1.School of Mechanical and Power Engineering，Henan Polytechnic University，Jiaozuo  454000，Henan，China;2.Henan Province Coal Mine Machinery Equipment Engineering Technology Research Center，Henan Polytechnic University，Jiaozuo  454000，Henan，China

Abstract:In order to study the influence of the disturbance of the drill pipe drilling on the borehole wall instability and failure of the gas drainage in-seam borehole，the calculation formula of the stress component of the friction sliding contact between the drill pipe and borehole wall was derived based on the Hertz contact theory.The analysis and calculation model of the composite stress field near the borehole wall under the disturbance of drill pipe drilling was established，the composite stress field of borehole wall of the gas drainage bedding hole was analyzed，and the calculation results were verified by the finite element analysis software Abaqus.Finally，according to the Mohr-Coulomb strength criterion，the critical drilling parameters to prevent the borehole wall instability were analyzed.The results showed that the maximum principal shear stress of the borehole wall reached the maximum when the drill pipe was located directly below borehole.The maximum principal shear stress was located on the contact surface.If it exceeded the shear strength of coal，the shear failure would occur.Reducing the revolution rate of the drill pipe and the friction coefficient between the drill pipe and the borehole wall could improve the stability of borehole wall during the drilling process of the gas drainage bedding hole.The larger the annulus gap between the drill pipe and the borehole wall was，the smaller the critical axial pressure was.The research results provided theoretical guidance for the selection of drilling process parameters of the gas drainage in-seam borehole.

Key words:drill pipe disturbance;gas drainage in-seam borehole;borehole wall instability;Mohr-Coulomb criterion;Hertz contact

 钻杆钻进扰动下顺层瓦斯抽采钻孔孔壁失稳机制_韩晓明.pdf