Research on process parameters of directional hydraulic punching considering creep effect in composite coal seam

With the increasing depth of coal mining and the difficulty of gas control in China, the technology of directional hydraulic punching to enhance gas extraction in composite coal seam has been widely promoted and applied. In order to further improve the efficiency and effectiveness of directional hydraulic punching in composite coal seam, we carry out the study on the influence of coal rock creep effect on parameters such as directional punching pressure relief time, punching spacing, and punching diameter; based on the theory of creep effect and actual on-site conditions, a simulation scheme for directional punching process parameters considering creep effect is proposed, the influence of creep effect on directional hydraulic punching is compared and analyzed by numerical simulation, the process parameters of directional punching considering creep effect is designed and verified through on-site experiments. The results indicate that, compared to the Mohr Coulomb model, the simulation results of considering creep effect are more in line with the actual situation on site; when the creep effect is considered, the pressure relief zone, plastic zone, and creep displacement range around the directional hydraulic punching hole in the composite coal seam increase with the increase of creep time and punching diameter, and the time required for coal rock creep and pressure relief between boreholes increases with the increase of borehole spacing; based on the on-site situation and the simulation results of composite coal seam directional punching parameters considering creep effect, the designed punching pressure is 26 MPa and the spacing between holes is 6 m; the creep range has covered the coal and rock between the boreholes within 30 days of directional punching in the composite coal seams, and different degrees of pressure relief have appeared the creep range, which has greatly shortened the period of pressure relief and gas extraction, and at the same time, it has improved the efficiency of hydraulic punching. The research on process parameters of the directional hydraulic punching technology considering creep effect in composite coal seam is expected to further improve the efficiency of pressure relief and gas extraction.