Abstract: Negative-pressure extraction is one of the most important factors affecting the seepage law of coal gas in the perforated hole. To study its influence, the gas flow in the hole was determined by designing a similar simulation test platform for gas seepage. Moreover, the numerical software was used to analyze the gas seepage in the coal around the hole. Combined with the above conclusions, the percolation characteristics of gas in the coal around the hole was studied. The results showed that the negative pressure was used to provide the power for gas seeping from the coal to the borehole. When the negative pressure was set in the range of 25~35 kPa, the Reynolds number was concentrated between 10 and 20. Thus, the low-speed turbulent flow is ensured, which was conducive to extracting the gas efficiently. With the increase of pumping time, the effect of negative pressure on the gas extraction gradually became weak, and the gas flow showed a negative exponential decay with time. The saturated value of coal seepage velocity was between 7.41×10?6 m/s and 1.30×10?5 m/s. The internal viscous resistance of the coal body inhibited the gas seepage. With increasing the negative-pressure extraction, the negative pressure of the borehole increased faster than that in the coal around the hole, which indicated the effect of the negative pressure on the borehole was more significant.

Key words: negative pressure, drilling, seepage characteristics, gas flow, pores and fissures