Experimental Study on Coal Gas Desorption Characteristics at Different Pressures at the Initial Stage of Borehole Drilling.

There are numerous constraints in conducting on-site experiments on the characteristics of gas emissions from boreholes in underground coal mines. Hence, it holds great significance to carry out experimental studies on gas emissions from boreholes in the laboratory. However, some of the conditions of the previous experimental systems employed differ from those in the field; especially, the drill bit used in actual coal mining borehole drilling and the diameter of the drilled hole are not unified, and the size of the borehole and drill bit affect the gas emission characteristics. In response to the above circumstances, this paper proposed and developed a physical simulation experimental system for a coal borehole drilling experimental system; the borehole and drill bit size were close to the actual engineering situation. The coal seam gas pressure was chosen, which directly influences the risk index of coal and gas outburst; experiments on the characteristics of gas emission from boreholes under different adsorption pressure conditions were conducted. The results indicated that the gas emission volume from the borehole increased with the increase of adsorption equilibrium pressure. The initial gas emission model conformed to the exponential decay model. The gas emission velocity initially rose and then remained stable. Under conditions of higher adsorption pressure, it took longer for the borehole gas emission velocity to reach stability. The developed experimental system provides technical conditions for the follow-up laboratory study of gas emission in coal cutting borehole drilling. The research results provide technical conditions for follow-up studies on gas emission in coal cutting boreholes and a basis for further development of the characteristics of gas emission in briquette boreholes.