Clay minerals are abundant in shale, characterized by a lamellar structure and dimensions smaller than a micron, giving rise to nanometer‐scale pore sizes and large specific surface area. They are commonly associated with water. However, the spatial distribution of the unsaturated water in clay is not very well understood, which significantly affects the subsequent shale gas flow capacity. Wettability heterogeneity in the presence of hydrocarbons further complicates the water distribution in clay. In this study, we use a 3‐D lattice Boltzmann model to study water adsorption and condensation in a reconstructed clay microstructure based on broad‐ion‐beam scanning electron microscopy images. Three wettability conditions are considered including a water‐wet case, a water‐repellent case, and a mixed‐wet case. The spatial distribution of the condensed liquid water phase is visualized, and the connectivity of the remaining open pore spaces is characterized. For the water‐wet case, water preferentially condenses in the small and narrow pore spaces, while the water‐repellent case reports the opposite trend. The mixed‐wet case results in mixed behavior, and connectivity of the pore space is bound by the former two cases. We then study the subsequent methane flow capacity with the presence of water for these three cases, and the calculated methane relative permeability curves show a percolation threshold for the water‐wet case, which is in good agreement with available experimental data in the literature measured on geosynthetic clay liners.

中文翻译：

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润湿性非均质性条件下粘土中水吸附及甲烷的迁移的孔隙尺度研究

泥质矿物在页岩中含量丰富，其特征为层状结构且尺寸小于微米，从而产生了纳米级孔径和较大的比表面积。它们通常与水相关。但是，人们对粘土中不饱和水的空间分布不是很了解，这严重影响了随后的页岩气流量。在烃存在下的润湿性非均质性进一步使粘土中的水分布复杂化。在这项研究中，我们使用3D格子Boltzmann模型，基于宽束电子束扫描电子显微镜图像，研究了重构粘土微结构中的水吸附和凝结。考虑了三种润湿性条件，包括水湿箱，防水箱和混合湿箱。可视化冷凝的液态水相的空间分布，并表征了其余开放孔隙空间的连通性。对于水润湿的情况，水优先在狭窄的狭窄孔隙中凝结，而斥水的情况则相反。混合-湿的情况导致混合的行为，并且孔隙空间的连通性受前两种情况的约束。然后，我们针对这三种情况研究了有水存在时的后续甲烷流量，并且计算出的甲烷相对渗透率曲线显示了水湿情况下的渗流阈值，这与文献中测量的可用实验数据高度吻合。土工合成的粘土衬里。对于水润湿的情况，水优先在狭窄的狭窄孔隙中凝结，而斥水的情况则相反。混合-湿的情况导致混合的行为，并且孔隙空间的连通性受前两种情况的约束。然后，我们针对这三种情况研究了有水存在时的后续甲烷流量，并且计算出的甲烷相对渗透率曲线显示了水湿情况下的渗流阈值，这与文献中测量的可用实验数据高度吻合。土工合成的粘土衬里。对于水润湿的情况，水优先在狭窄的狭窄孔隙中凝结，而斥水的情况则相反。混合-湿的情况导致混合的行为，并且孔隙空间的连通性受前两种情况的约束。然后，我们针对这三种情况研究了有水存在时的后续甲烷流量，并且计算出的甲烷相对渗透率曲线显示了水湿情况下的渗流阈值，这与文献中测量的可用实验数据高度吻合。土工合成的粘土衬里。