Study on physical simulation experiment of hydraulic borehole flushing and pressure released and permeability improved effect

Ln order to study the pressure released and permeability improved mechanism of the hydraulic borehole flushing and effectively solve a gas drainage pr oblem in a single soft and low permeability seam, a self researched and developed physical simulation experiment system of the hydraulic borehole flushing was applie d to conduct the experiment of the hydraulic borehole flushing under the condition of the different rotary speed. A gas pressure evolution law during the seam gas drain age process before and after the hydraulic borehole flushing was compared and an analysis was conducted on the hydraulic borehole flushing function affected to the t arget scope of the seam gas drainage. The study results showed that with the flushing rotary speed increased, the flushed coal quantity from the borehole, an equivalen t radius of the flushed borehole and the pressure released radius of the flushed borehole were increased and thus the gas drainage target scope was increased under t he same time condition of the gas drainage. The pressure released radius of the flushed borehole would be high in a high direction of the geostress and would be low in a low direction of the geostress. The pressure released radius of the flushed borehole was 1.6 ~ 2.0 times larger than the equivalent radius of the flushed borehole. Wit hin the pressure released radius of the flushed borehole, during the initial period of the gas drainage, the gas pressure decreased speed rate was obviously increased. Beyond the pressure released radius of the flushed borehole, during the initial period of the gas drainage, the gas pressure decreased speed rate was not obvious . After a time period of the gas drainage operation, the gas pressure decreased speed rate was obviously increased. The form of the gas drainage target region was similar to the form of the flushed borehole pressure released scope and would similarly be an ellipse on the cross section of the vertical borehole.