Investigation and experimentation research on extraction radius of segmented hydraulic cavitation borehole in mining-coalbed

Aiming at the problem of unclear definition and the difficulty to determine the drilling radius of segmental hydraulic cavity drilling in coal seam, taking No. 3 coal seam in Gucheng Coal Mine as the engineering background, the field test study on the drilling radius of hydraulic hole drilling in coal seam was carried out. In conjunction with on-site monitoring of gas drainage flows from different test boreholes, the gas reserve method was used to investigate the extraction radius of the hydrodynamic cavity boreholes and ordinary boreholes in this coal seam. The time varying law of the extraction radius of different types of experimental boreholes and the increase of gas extraction radius from the hydrometric boreholes in coal seam were obtained. The results show that：①In the same extraction time,the average extraction quantities of the forward-type coal seam segmented hydraulic hole-drilling boreholes and the backward-type coal seam segmented hydraulic hole-drilling boreholes are 3.08 and 3.79 times higher than that of ordinary boreholes. And the gas drainage radius of progressive and retrusive hydraulic cavitation boreholes in coal seam are 2.14～5.62 times and 2.58～5.88 times higher than that of ordinary boreholes.The segmental hydraulic cavity drilling can significantly increase the pure volume of drilling gas extraction and effectively expand the drilling gas extraction radius and the lifting effect of the backward type coal seam segmented hydraulic cavern drilling is more significant;②The gas drainage radius of both the ordinary extraction borehole and the segmental hydraulic cavity borehole have time-varying characteristics, i.e. the drainage radius increases with the extension of time, and gradually tends to a certain limit value. After 240 d of drainage, the extraction radius of ordinary borehole basically reaches the limit, and only increased by about 0.01 m within 60 d, the gas flow in the borehole gradually depleted, and the extraction radius of segmented hydraulic cavitation borehole in coal seam can be still be effectively increased with time, and the gas flow rate remains stable, indicating that the effective extraction time and the extraction life of the segmental hydraulic cavity borehole is longer than that of a normal borehole.