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不同冲击倾向性煤体孔隙结构及瓦斯吸附特征研究

Study on pore structure and gas adsorption characteristics of coals with different burst liability

  • 摘要: 随着开采深度增加,煤层高地应力、低渗透、强扰动等特征逐渐显现,井下灾害形式愈发复杂,其中冲击地压与瓦斯突出是最主要的复合灾害表现形式。为研究不同冲击倾向性煤样微观孔隙结构与瓦斯吸附间的内在联系,利用瓦斯等温吸附实验和不同孔隙测试实验的优势孔径段思想,对不同冲击倾向性煤样进行孔隙联测。实验结果表明:煤体微观结构特征在一定程度上可反映煤层宏观构造破坏程度和应力作用性质,孔隙含量较少则煤样冲击倾向性较强,王庄煤样为强冲击倾向性煤样,其孔隙含量最少,结构致密、硬脆性更强,在受载过程中积聚更多应变能,高应力环境导致煤样中微孔占比较多;天池煤样为无冲击煤样,其大孔比例更高,同时在破碎粉化过程中煤样孔隙含量增幅最为明显。进一步通过瓦斯等温吸附实验,发现相同条件下余吾煤样的瓦斯吸附量最大,天池煤样次之,王庄煤样最小,复杂的孔隙结构和较差的孔隙连通性更有利于瓦斯赋存,强冲击倾向性煤体王庄煤样的孔隙连通性更强,这将有利于瓦斯的运移和释放。余吾煤样和天池煤样煤体破碎程度高,孔隙之间的通道被压窄或堵塞,形成部分小吼道连通大孔隙和封闭孔隙,孔径分布越集中,非均质性越强,孔隙复杂度越高,连通性越差,随粒径减少煤样瓦斯吸附增速更快。同时微孔结构参数与瓦斯吸附量相关性最高,其次为中孔,而大孔参数与吸附量无明显相关关系,且比表面积与吸附量的相关性普遍高于孔体积,表明孔隙表面是瓦斯吸附发生的主要场所。进一步根据全孔孔径分布计算多重分形维数特征值,极限吸附量的多少也可以通过多重分形维数特征值来表征,不同煤样的分形参数对瓦斯吸附量的影响存在差异性,余吾煤样、天池煤样的吸附量与α呈正相关关系,与H呈负相关关系,而值域最值f(α)max相关关系不明显。

     

    Abstract: With the increase of mining depth, the features of high geopathic stress, low permeability and strong disturbance of coal seams gradually appear, and the form of underground disasters becomes more and more complicated, among which impact ground pressure and gas protrusion is the most important form of composite disaster manifestation. In order to study the intrinsic connection between microscopic pore structure and gas adsorption of different impact-prone coal samples, pore co-testing of different impact-prone coal samples was carried out by utilizing gas isothermal adsorption experiments and the idea of advantageous aperture segments of different pore testing experiments. The experimental results show that: the microstructural characteristics of the coal body can reflect the degree of macroscopic tectonic damage and the nature of the stress action in the coal seam to a certain extent, and the coal samples with less pore content have stronger impact tendency; the Wangzhuang coal sample is a strong impact tendency coal sample, with the least pore content, a dense structure, stronger hardness and brittleness, and more strain energy accumulated in the process of loading, and the high-stress environment leads to a larger number of micropores in the coal samples; the Tianchi coal sample is a no-impact coal sample, with large pores, and its porousness is larger than that in the coal samples. Tianchi coal sample is a non-impacted coal sample, which has a higher proportion of large pores and the pore content of the coal sample increases most obviously during the crushing and pulverization process. Further, through the gas isothermal adsorption experiments, it was found that under the same conditions, the gas adsorption amount of the Yuwu coal sample was the largest, the Tianchi coal sample was the second largest and the Wangzhuang coal sample was the smallest, and the complex pore structure and poor pore connectivity were more favorable to the gas storage, and the strong impact tendency of the Wangzhuang coal sample had stronger pore connectivity, which was favorable to the transportation and release of the gas. The coal body of Yuwu coal sample and Tianchi coal sample has high degree of fragmentation, and the channels between the pores are narrowed or blocked, forming part of the small roar channel connecting the large pores and closed pores, and the more concentrated the distribution of pore sizes, the stronger the non-homogeneity, the higher the pore complexity, and the worse the connectivity, and the growth rate of gas adsorption with the reduction of the size of the coal sample is more rapid. Meanwhile, the correlation between microporous structural parameters and gas adsorption was the highest, followed by mesopore, while macroporous parameters had no obvious correlation with adsorption, and the correlation between specific surface area and adsorption was generally higher than that of pore volume, which indicated that the pore surface was the main place where gas adsorption occurred. The multiple fractal dimension eigenvalues were further calculated based on the pore size distribution of the whole pore, and the amount of limiting adsorption could also be characterized by the multiple fractal dimension eigenvalues, and the influence of fractal parameters on gas adsorption amount varied among different coal samples, and the adsorption amount of the Yuwu and Tianchi coal samples showed a positive correlation with α, and a negative correlation with H, whereas the value domain maximum value of f(α)max had no obvious correlation.

     

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