Abstract To improve the general understanding of diffusive processes in coal and investigate if representative reservoir properties can be estimated from measurements on crushed coal particles, adsorption and desorption experiments on crushed samples and large, intact core samples are carried out. Diffusion properties are analysed for methane, carbon dioxide and nitrogen up to a pressure of 10 MPa at a temperature of 35 °C. The samples are a low volatile bituminous coal and a medium volatile bituminous coal from Australia's Bowen Basin. A bidisperse model (a simplified version of the Ruckenstein model for micro-pore dominated flow), characterised by a ‘fast’ and a ‘slow’ fraction, is required to describe the observed diffusion behaviour. Results from the modelling show that effective diffusivities of the core samples are typically an order of magnitude lower than for the crushed coals, and the ‘slow’ effective diffusivities are typically at least one order of magnitude lower than the corresponding ‘fast’ effective diffusivities. A pressure dependency of the effective diffusivities is noted but an explicit relationship with gas content could not be established. This may be due to the experimental set-up, which does not eliminate the effect of differential pressure. Calculation of the diffusion path length for the coal core reveals that the diffusion path length in coal may not be constant but decreases with increasing matrix gas content as a result of coal swelling. Furthermore, there is a distinct difference between the diffusion paths derived from the ‘fast’ and the ‘slow’ fractions; the ‘slow’ diffusion path of the coal core is 100s of microns shorter than the ‘fast’ diffusion path. The faster diffusion associated with the longer diffusion path is interpreted to relate to micro-porosity, while slower diffusion via the shorter diffusion path is interpreted to relate to macro-porosity.

中文翻译：

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博文盆地（澳大利亚）煤中的 CH4、CO2、N2 扩散：煤芯和碎煤颗粒的吸附动力学之间的关系

摘要 为了提高对煤中扩散过程的一般认识，并研究是否可以通过对碎煤颗粒的测量来估计具有代表性的储层性质，对碎煤样品和大型完整岩心样品进行了吸附和解吸实验。在 35 °C 的温度下，分析了高达 10 MPa 压力的甲烷、二氧化碳和氮气的扩散特性。样品是来自澳大利亚博文盆地的低挥发分烟煤和中挥发分烟煤。双分散模型（微孔主导流的 Ruckenstein 模型的简化版本），以“快”和“慢”部分为特征，需要描述观察到的扩散行为。建模结果表明，岩心样品的有效扩散率通常比碎煤低一个数量级，“慢”有效扩散率通常至少比相应的“快速”有效扩散率低一个数量级。注意到有效扩散率的压力依赖性，但不能建立与气体含量的明确关系。这可能是由于实验设置没有消除压差的影响。煤芯扩散路径长度的计算表明，煤中的扩散路径长度可能不是恒定的，而是随着煤膨胀导致基质气体含量的增加而减小。此外，源自“快”和“慢”部分的扩散路径之间存在明显差异；煤芯的“慢”扩散路径比“快”扩散路径短 100 微米。与较长扩散路径相关的较快扩散被解释为与微孔隙度相关，而通过较短扩散路径的较慢扩散被解释为与大孔隙度相关。