Abstract
The gas emission rate of boreholes is one of the most important indices for coal and gas outburst prediction. In this work, instantaneous gas emission velocity and environmental effects on borehole gas emission were studied. Through theoretical analysis, the mechanism of crack propagation in the coal borehole was clarified, and the effect of soft and hard coal on gas desorption and gas emission. The results of numerical simulations also indicated that the initial gas emission has a function relationship to the drilling distance and the physical characteristics of the coal seam. A novel dynamic testing technology was proposed to obtain gas emission velocity. Laboratory experiments under adsorption and desorption of CO2 and N2 were performed using coal samples from Xuehu, Fenghui, Weishe, and Wuzhong coal mines. The data of initial gas emission under different coal samples were recorded, and the fitting curves were obtained. The results show a positive correlation between initial gas emission and drilling depth. However, abnormal would occur when the drill pipe enters the soft stratification, and the maximum value of the initial gas emission of the abnormal part is 3.8 times the normal value, which indicates a high degree of sensibility to soft stratification. The results were revealed the dynamic gas emission law of boreholes.
Highlights
Various accidents such as coal and gas outbursts, gas explosions and fire generally occur in coal mining [1,2,3,4,5,6]
The initial gas emission was tested with coal samples from different coal mines
It revealed the influence of the physical properties of the coal seams on gas emission from boreholes
Summary
Various accidents such as coal and gas outbursts, gas explosions and fire generally occur in coal mining [1,2,3,4,5,6]. A number of scholars have researched on the law of coal seam gas flow It shows that the maximum rate of gas output from drilling occurs a few seconds before the coal body is destroyed, and the gas diffusion rate of tectonic coal at the initial stage of diffusion is greater than that of the primary coal. Research on gas emission from boreholes shows that the rate of velocity change is largest at the initial moment, and it increases with the gas adsorption pressure of coal seams [37]. Previous studies focused on the gas emission model of exposure coal body, which simulates the effect of ground stress, gas pressure, and coal seam permeability on initial gas emission in a static state. The laboratory experiment under determination of initial gas emission was presented in this work and verify the accuracy of the numerical simulation
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