Evolution law of air leakage and oxidation characteristics of surrounding coal body in bedding gas extraction

Abstract

To explore the development of coal seam fractures around gas extraction borehole and the issue of self-ignition caused by air leakage, a combination of theoretical analysis, field testing, and laboratory experiments was used. The distribution characteristics of cracks in the crushed zone after borehole excavation were analyzed. An in-situ test using SF6 tracer gas was conducted to measure air leakage in the gas extraction borehole, revealing the law of air leakage around the gas extraction borehole during the process of gas pre-extraction. Using a program for temperature increase and gas chromatography combined experiment, the self-ignition characteristic parameters of coal under different air supply rates were studied as a research object of the 215 working face in a certain mine, and the functional relationship formula between oxygen consumption rate, CO generation rate, and coal temperature and air supply rate was obtained. The results showed that the main ways of air leakage around the gas extraction borehole were side leakage of roadway coal wall, drilling fracture leakage, and sealing section leakage. The minimum air leakage rate around the gas extraction borehole was quantitatively obtained between 0.19 m/min and 0.68 m/min, with an average air leakage rate of 0.41 m/min, and the range of air leakage in the borehole was greater than 4.35 m. The air supply rate had a promoting effect on the natural characteristics parameters of coal.

Keywords

• coal spontaneous combustion
• gas extraction
• drilling air leakage
• air leakage law
• influence law