Study of the law of gradual change of the influence of hydraulic punching under a rational coal output

Abstract

In low permeability and soft coal seams, the boreholes are often blocked due to the rheology of coal, which leads to low flow and gas concentrations. Therefore, additional measures are needed to artificially increase the permeability of coal seams, such as hydraulic flushing. The application of hydraulic punching in the “three-soft” coal seam in the Dengfeng coal mine is the first time. According to numerical simulation, the range of the effect on the coal output was obtained from hydraulic punching. Simulation results show that the coal amounts from punching out are 0.5 t/m, 0.7 t/m, 1.0 t/m, and 1.2 t/m, and after gas extraction for 3 months, the effective radii are 5.6 m, 6.4 m, 7.1 m, and 7.4 m, respectively. Through a comparison with the actual situation in the field, it is determined that the rational coal output from hydraulic punching is 0.7 t/m. In addition, the gradient law of the effective range of hydraulic flushing was obtained. By comparison, the absolute error between the predicted data and the measured data is between 0.05 and 0.24 m, and the relative error is between 1 and 8%, which can meet the needs of the project, guiding the field test of hydraulic punching.