中尺度煤块中煤层气多尺度扩散系数随时间依赖的实验及模型

Experiment and Model of Multi-scale Diffusion Coefficient of Coal Bed Methane with Time Dependence in Mesoscale Coal

为探究煤层气含气量(和储量)测定过程中混有中尺度(厘米级)煤块的影响,开展了不同煤种的毫米-厘米级中等尺度煤块在不同压力下的煤层气扩散实验。实验发现,扩散前期实验扩散率大于经典模型的理论扩散率,扩散后期实验扩散率小于经典模型的理论值。全时扩散过程中扩散系数并非一个常数,而是随时间延长而衰减的函数。提出了能精确描述不同气压下不同煤种中尺度煤块的煤层气扩散全过程的动扩散系数新模型。与以往实验相比,中尺度煤块的初始扩散系数比粉煤大1～2个数量级,而扩散系数衰减系数比粉煤小1～2个数量级,原因是中尺度煤块包含了更大的孔裂隙,而其孔径级差较小。

To investigate the effect of mesoscale coal(centimeter-scale) on coal bed methane content(reserve)in the process of determination, the experiment of coal bed methane diffusion of mesoscale coal,millimeter-centimeter, were carried out under different pressures. The results indicate that experimental diffusion rate is larger than the theory during initial stage, but the result is opposite during later stage.The diffusion coefficient of gas in coal is not a constant, but it decreases with time increasing.According to experiment, a new diffusion model of time-dependent dynamic diffusion coefficient is proposed. Compared with previous experiments, the initial diffusion coefficient of mesoscale coal is higher than that of pulverized coal particles 1 to 2 order of magnitude, the decay coefficient of diffusion coefficient is smaller than that of pulverized coal particles 1 to 2 order of magnitude. The reason is that the mesoscale coal contains a larger pore fissure, and its aperture differential is smaller.