A new laboratory method for accurate measurement of the methane diffusion coefficient and its influencing factors in the coal matrix
A new laboratory method for accurate measurement of the methane diffusion coefficient and its influencing factors in the coal matrix
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准确测量煤基质中甲烷扩散系数及其影响因素的实验室新方法
DOI：
10.1016/j.fuel.2015.05.046
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发表时间：
2015-10-15
期刊：
影响因子：
7.4
通讯作者：
Tao, Shu
中科院分区：
文献类型：
--
作者：
Xu, Hao;Tang, Dazhen;Tao, Shu
扩散系数是评价煤基质甲烷扩散特性的重要参数。然而，目前的甲烷扩散系数测量技术，包括颗粒法、稳态法和反扩散法，都存在一定的局限性。例如，样品的孔隙结构容易被破坏，测试时间长。此外，在不同的测试原理和条件下，不同方法的结果缺乏可比性。提出了一种新的煤基质中甲烷扩散系数的实验室测定方法，即用煤基质薄片代替煤颗粒作为被测样品，并分析了瓦斯压力、煤阶和水分含量等因素对甲烷扩散系数的影响。结果表明，该方法能较好地保持煤基质的固有空间结构，计算出的甲烷在煤基质中的扩散系数在10（11）~ 10（-9）m（2）/s量级，与实际储集层的数值接近。在相同温度下，瓦斯压力越大，甲烷扩散系数越大，而与煤的含水饱和度和煤阶无关。煤的吸附量随煤变质程度的增加而增加，甲烷在煤基质中的扩散系数随煤变质程度的增加呈现先降后升的“U”型变化趋势。此外，水分对甲烷扩散系数有重要影响。水分的增加会降低基质对甲烷的吸附能力，这使得难以形成较大的浓度梯度，因为干燥样品的扩散系数高于饱和水样的扩散系数。(C)2015爱思唯尔有限公司版权所有。
The diffusion coefficient is a key parameter for evaluating the methane diffusion properties of a coal matrix. However, all of the current measurement technologies for methane diffusion coefficients, including the particle method, the steady state method and the inverse diffusion method, have certain limitations. For example, the pore structure of the sample is easily destroyed, and the test time is long. Moreover, the results from different methods lack comparability under the various test principles and conditions. In this work, a new laboratory method for measuring the methane diffusion coefficient in coal matrixes was proposed, where coal matrix flakes instead of coal particles were used as the samples to be measured, and the factors influencing methane diffusion coefficients such as gas pressure, coal rank and moisture content were also analyzed. The results indicate that this new method can keep the intrinsic space structure of the coal matrix and yields methane diffusion coefficients on the order of 10(11)-10(-9) m(2)/s in coal matrix, which are close to realistic reservoir values. Under the same temperature, methane diffusion coefficients increase with increasing gas pressure regardless of the water saturation and coal rank. Additionally, the adsorption capacity increases when the metamorphic degree of coal increases, while the methane diffusion coefficient in coal matrixes exhibit a trend of first dropping and then rising ("U" shape) with an increase in coal rank. Moreover, moisture has an important effect on the methane diffusion coefficient. Increasing moisture can reduce the matrix adsorption capacity for methane, which makes it difficult to form a larger concentration gradient because the diffusion coefficients of dry samples are higher than those of the saturated water samples. (C) 2015 Elsevier Ltd. All rights reserved.