Methane diffusion is a very important gas-transport mechanism in shales. Meanwhile, one of the biggest differences between shale gas reservoirs and conventional gas reservoirs is a multiscale pore structure in the former. Two kinds of methane diffusion experiments are conducted in this work to measure methane diffusion coefficients in shale cores at supercritical conditions. Experimental results show that (1) a free molecular diffusion coefficient is averaged to be 1.214 × 10⁻¹⁰ m²/s at reservoir conditions from the isobaric diffusion experiments; (2) however, the Knudsen diffusion, surface diffusion and configurational diffusion coefficients in the pressure decay experiments are more significant for shale gas development. It is presented that Knudsen diffusion and surface diffusion appear simultaneously as gas transports in matrix nanopores, the mean diffusion coefficients of which are 4.99 × 10⁻¹⁴ m²/s for pores of a diameter smaller than 4 nm and 9.03 × 10⁻⁹ m²/s for pores of a diameter bigger than 4 nm. The mean configurational diffusion coefficient for dissolved gas is calculated as 2.06 × 10⁻²² m²/s. In addition, the four types of diffusion coefficients mentioned above are also theoretically calculated through their corresponding models to compare with the experimental results. Due to the measured methane diffusion coefficients corresponding to a wide range of pore sizes, a relationship between gas diffusion and pore size is obtained by the combination of theoretical and experimental results, and this can guide to further analyze the comprehensive diffusion behavior in shale gas development, as well as the relative contribution of each diffusion during different production stages. This work sheds light on the gas diffusion behavior over multiple pore sizes, which is beneficial for further quantitatively understanding shale gas transport in matrix during production.

甲烷扩散是页岩中非常重要的气体传输机制。同时，页岩气藏与常规气藏之间最大的区别之一是前者的多尺度孔隙结构。在这项工作中进行了两种甲烷扩散实验，以测量超临界条件下页岩岩心中的甲烷扩散系数。实验结果表明（1）自由分子扩散系数平均为1.214×10 ^-10  m ²/ s在等压扩散实验中的储层条件下；（2）然而，在压力衰减实验中的克努森扩散，表面扩散和构型扩散系数对于页岩气的开发更为重要。结果表明，克努森扩散和表面扩散同时在基质纳米孔中作为气体传输而出现，对于直径小于4 nm和9.03×10 ^-9  m的孔，其平均扩散系数为4.99×10 ^-14  m ² / s对于直径大于4 nm的孔为² / s。溶解气体的平均构型扩散系数计算为2.06×10 ^-22  m ²/ s。另外，理论上还通过相应的模型计算了上述四种扩散系数，并与实验结果进行了比较。由于测得的甲烷扩散系数对应于较宽的孔径范围，因此通过理论和实验结果的结合得出了气体扩散与孔径之间的关系，这可为进一步分析页岩气开发中的综合扩散行为提供指导。 ，以及每个扩散在不同生产阶段的相对贡献。这项工作揭示了气体在多种孔径上的扩散行为，这有助于进一步定量地了解生产过程中页岩气在基质中的传输。