Research and application of water jet and cooperative repair technology in gas drainage

Gas drainage boreholes generally have the problems such as blockage and poor drainage effects due to deformation, cinder accumulation, and borehole collapse. By analyzing the mechanism of borehole collapse instability, it was concluded that the properties of coal and rock mass, geological structure and multi-stress coupling condition were the main factors causing borehole instability, and then the situation of the corresponding blocked borehole section was deduced. By the action of high pressure water jet to solve the blockage, this paper put forward the technology of water jet dredging and screen pipe borehole collaborative repair, and a lightweight pneumatic drilling repair equipment was developed. The application results show that the cooperative repair technology can effectively solve the technical problem that the gas extraction borehole can’t be effectively extracted after drainage borehole collapses, the test borehole repair depth reaches 50 m, after repair, the concentration and pure flow of gas in single borehole extraction increased by 0.57 times to 3.67 times and 0.99 times to 5.15 times compared with that before repair, the drainage effect has been greatly improved, the quick and convenient repair of the collapsed and blocked borehole is realized to ensure the smooth gas flow channel.