Abstract
Abstract The development of coal seam fissures and gas migration process caused by mining disturbance has an extremely important influence on gas control and roadway stability. In this study, the desorption, diffusion, and migration tests of adsorbed gas under the coupling effect of temperature and uniaxial compression were conducted on four coal samples from Zhangxiaolou mine, using the temperature and pressure coupling test system of deep coal rocks. The test confirms that the higher the temperature, the faster the desorption and emission of the adsorbed gases in the coal, and the larger the volume of the emitted gases. Meanwhile, it is found that the adsorbed gases in the coal samples of Zhangxiaolou mine are carbon dioxide and methane in the order of content. It is found that during the uniaxial compression process, several large negative values of the pressure of the emitted gas occur during the stable growth stage of the crack. This indicates that the crack expansion makes a new negative pressure space inside the coal sample, and the negative pressure values increase continuously during the unstable growth phase of the crack until the coal sample is destroyed. And after the axial pressure is removed, the escaped gas pressure shows a large positive value due to the rebound of the coal matrix and the continuous desorption of a large amount of adsorbed gas from the new crack location, which has a significant hysteresis with respect to the occurrence of the peak stress. Meanwhile, the SEM images of the coal samples before and after the test are analyzed to confirm the cause of the negative pressure generation.
Highlights
The mechanical environment of deep coal rocks is very complex, with three highs and one disturbance [1], where the three highs refer to high stress, high temperature, and high permeability, and the one disturbance refers to the disturbance force caused by mining disturbance in deep engineering
Gas reflux caused by volume expansion occurs, which is called “negative pressure effect.”
The following conclusions were reached: (1) The desorption and diffusion characteristics of adsorbed gas under the coupling effect of temperature and pressure were measured by using the deep coal sample adsorption gas test system on coal samples from Zhangxiaolou mine
Summary
The mechanical environment of deep coal rocks is very complex, with three highs and one disturbance [1], where the three highs refer to high stress, high temperature, and high permeability, and the one disturbance refers to the disturbance force caused by mining disturbance in deep engineering. Many studies have been done on the adsorption and desorption of coal and gas, there are still few studies on the desorption, diffusion, and transport behavior of adsorbed gas in coal from the conditions of the coupling effect of temperature and pressure [32,33,34,35,36]. Considering the combined effects of increasing coal mining depth and increasing coal mine working face temperature and high ground stress, coal seam adsorptive gas keeps desorption and diffusion to the working face under the action of temperature and pressure, which seriously endangers personnel safety. The innovation of this experiment is to combine the temperature and pressure environment in which the coal samples are located and to obtain the influence law of temperature and pressure on gas desorption migration from the perspective of the experiment, and the results obtained from the experiment have important theoretical and cognitive significance for guiding the coal seam gas extraction and reducing the hidden gas hazard in coal mines
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