Yan Jiangwei, Feng Xiang, Guo Yan, Wang Wei, Wu Lei, Tan Zhihong
State Key Laboratory Cultivation Base for Gas Geology and Gas Control, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
School of Safety Science and Engineering, Henan Polytechnic University, Jiaozuo, Henan 454003, China.
ACS Omega. 2021 Aug 19;6(34):22114-22125. doi: 10.1021/acsomega.1c02706. eCollection 2021 Aug 31.
Understanding gas desorption effects and laws of coal mass under different conditions is essential for the effective exploration of gas emission in underground coal mines, prediction and prevention of coal and gas outburst, accurate detection of gas [coal methane (CBM)] content in coal seams, and prediction of CBM productivity. Using a self-developed test platform, we simulated gas adsorption and desorption and performed physical simulation tests. Based on these tests, we investigated the differences in the total amount of gas desorbed, desorption rate, and initial amount of gas desorbed by long-flame coal, coking coal, meager-lean coal, and anthracite on different scales under different gas pressures. Two methods are used for compensating gas loss, namely, the method and the power function method, as stipulated in the current Standards for Determination of Gas Content in Coal Seams in China. By combining these two methods, we analyzed the applicability of these two compensation methods in coal on different scales with varying degrees of metamorphism under gas pressures. The results demonstrated that (1) under the same gas adsorption pressure, the cumulative total amount of gas desorbed per unit mass within 90 min for the four kinds of coal samples increases with the degree of metamorphism. Changes in the cumulative amount of gas desorbed per unit mass and the desorption rate with the degree of metamorphism vary with stages. Notably, a higher adsorption pressure leads to a more obvious stage change. (2) Under the same gas adsorption pressure, the cumulative total amount of gas desorbed per unit mass and the desorption rate of coal with the same degree of metamorphism are inversely proportional to the size of the coal sample. This indicates significant scale effects. The larger the degree of metamorphism and gas adsorption pressure, the more significant are the scale effects of gas desorption. (3) For coal with the same degree of metamorphism, the higher gas adsorption pressure leads to a larger cumulative total amount of gas desorbed and a higher desorption rate throughout the desorption process and a larger proportion of the cumulative amount of gas desorbed in the initial stage. The smaller the size of the coal sample, the more obvious the pressure effects of gas desorption are. (4) For coal samples with the same degree of metamorphism, when the gas content in coal seams is kept constant, the larger the size of the coal sample, the smaller the actual gas loss is. Moreover, a higher gas content in coal seams results in a greater gas loss and a larger calculation error for gas loss. Compared with the method, the power function method reveals a smaller deviation between the calculated gas loss and the actual gas loss, which is found to be more accurate. A larger size coal sample results in higher accuracy in the calculated gas loss.
了解不同条件下煤体瓦斯解吸效应及规律，对于有效勘探煤矿井下瓦斯涌出、预测和防治煤与瓦斯突出、准确检测煤层瓦斯（煤层气，CBM）含量以及预测煤层气产能至关重要。利用自主研发的试验平台，模拟瓦斯吸附和解吸过程，并进行了物理模拟试验。基于这些试验，研究了长焰煤、焦煤、贫瘦煤和无烟煤在不同瓦斯压力下不同尺度上瓦斯解吸总量、解吸速率和解吸初始瓦斯量的差异。采用我国现行《煤层瓦斯含量测定方法》规定的两种瓦斯损失量补偿方法，即方法和幂函数法。通过结合这两种方法，分析了这两种补偿方法在不同变质程度、不同尺度煤样在瓦斯压力作用下的适用性。结果表明：（1）在相同瓦斯吸附压力下，4种煤样在90min内单位质量瓦斯解吸累积总量随变质程度的增加而增大。单位质量瓦斯解吸累积量和解吸速率随变质程度的变化呈现阶段性变化，且吸附压力越高，阶段性变化越明显。（2）在相同瓦斯吸附压力下，相同变质程度煤的单位质量瓦斯解吸累积总量和解吸速率与煤样尺寸成反比，表明存在显著的尺度效应。变质程度和瓦斯吸附压力越大，瓦斯解吸的尺度效应越显著。（3）对于相同变质程度的煤，较高的瓦斯吸附压力导致整个解吸过程中瓦斯解吸累积总量越大、解吸速率越高，且初始阶段瓦斯解吸累积量所占比例越大。煤样尺寸越小，瓦斯解吸的压力效应越明显。（4）对于相同变质程度的煤样，当煤层瓦斯含量保持不变时，煤样尺寸越大，实际瓦斯损失越小。且煤层瓦斯含量越高，瓦斯损失越大，瓦斯损失计算误差越大。与方法相比，幂函数法计算的瓦斯损失量与实际瓦斯损失量之间的偏差较小，结果更准确。煤样尺寸越大，瓦斯损失量计算精度越高。
