The demand on energy is rising and shale gas as an important unconventional energy resource has received worldwide attention. It has shown a significant effect on the world's energy structure after the commercial exploitation of shale gas in the United States. Understanding diffusion and permeation of shale gas at geological depths is quite essential, but it cannot be described by traditional Fick or Knudsen diffusion models. In this work, we use dual control volume–grand canonical molecular dynamics method to systematically investigate the permeation process of shale gas in montmorillonite (i.e., a clay mineral of shale) at different geological depths. Results indicate that temperature, pressure, and pore size have an important effect on the permeability, and Knudsen equation cannot describe the permeability of shale gas. Accordingly, on the basis of these simulated data, we propose a new mesoscale model to describe the permeability of shale gas at geological depths. The new mesoscale model shows extensive applicability and can excellently reproduce the extrapolation testing data, and it satisfactorily bridges the gap between Knudsen diffusion and Fick diffusion, which provides important fundamentals for exploitation of shale gas. © 2017 American Institute of Chemical Engineers AIChE J, 2017

中文翻译：

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页岩气在地质深度扩散和渗透的中尺度模型

对能源的需求正在上升，页岩气作为一种重要的非常规能源已受到全世界的关注。在美国页岩气的商业开发之后，它对世界的能源结构产生了重大影响。了解页岩气在地质深度的扩散和渗透是非常重要的，但是传统的Fick或Knudsen扩散模型无法描述它。在这项工作中，我们使用双重控制体积-大规范分子动力学方法系统地研究了不同地质深度的蒙脱石（即页岩的黏土矿物）中页岩气的渗透过程。结果表明，温度，压力和孔径对渗透率具有重要影响，而Knudsen方程无法描述页岩气的渗透率。因此，在这些模拟数据的基础上，我们提出了一个新的中尺度模型来描述页岩气在地质深度的渗透率。新的中尺度模型显示出广泛的适用性，并且可以很好地再现外推测试数据，并且令人满意地弥合了克努森扩散和菲克扩散之间的差距，这为页岩气的开采提供了重要的基础。©2017美国化学工程师学会AIChE的Ĵ，2017年