Study on permeability enhancement by hydraulic punching in crossing boreholes and comprehensive testing method for effective radius of gas extraction

To clarify the applicability of this parameter in Changping Coal mine, a comprehensive evaluation operation including the pressure drop measurement, tracer gas indication, and numerical simulation was adopted to validate of the effectiveness of the extraction radius of crossing boreholes based on the same drilling layout and testing conditions.Field test was applied to investigate the extraction effect of crossing boreholes at different spacing.The accuracy of the developed comprehensive evaluation method was evaluated.The pumping effect of different spacing crossing boreholes was also examined by field tests, the results show that: using crossing boreholes hydraulic flushing measures, its effective radius reaches 3.5 m when pumping time is 180 d; the total amount of pumping for 7.0 m drill hole spacing is 1.10, 1.07, 1.28 times of the drill hole spacing of 5.0 m, 6.0 m, and 8.0 m, respectively, which achieves a better effect of the engineering practice; the comprehensive research method is accurate and reliable.