Abstract Shale gas is usually a multi-component gas mixture dominated by CH4. Moreover, CO2 sequestration in shale reservoirs and CO2-enhanced shale-gas recovery also result in multi-component gas flow in shale reservoirs. Therefore, compared with single-component gas flow, multi-component gas flow is more often encountered in practice. Furthermore, shale rock contains a lot of nano-pores in which the micro-scale effect makes the multi-component gas flow become more complex. In this paper, the lattice Boltzmann method is employed to simulate the two-component shale gas flow in a two-dimensional micropore under different conditions. The pore-scale transport mechanism of the two-component shale gas is investigated and the gas separation phenomenon for the shale gas flow is discussed in detail. It is found that the molar fraction of each species in shale gas does not distribute uniformly along the micropore and the gas separation phenomenon exists in the two-component pressure-driven shale gas flow. The molar fraction distribution of each species along the micropore is affected by the Knudsen number, pressure ratio, shale gas composition and molar fraction of each species for the pressure-driven gas flows. In particular, we find that the molar fraction distribution and pressure distribution for two-component shale gas along the micropore are related to the pressure ratio and are unrelated to the pressure gradient. With increasing the molar fraction of CH4 in shale gas, both the gas-mixture velocity at the outlet and the slip velocity along the micropore become larger. Both the Knudsen number and pressure ratio affect the molar fraction distribution of CO2 for the CH4 CO2 mixture in the micropore during CO2 injection, while the influence of them works oppositely. Furthermore, the concentration diffusion without the external force is affected by the micropore width and the concentration difference between the gas mixtures.

中文翻译：

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双组分页岩气流的孔隙尺度晶格 Boltzmann 模拟

摘要 页岩气通常是一种以CH4 为主的多组分混合气。此外，页岩储层中的 CO2 封存和 CO2 增强的页岩气采收也导致页岩储层中的多组分气流。因此，与单组分气流相比，多组分气流在实际应用中更为常见。此外，页岩中含有大量纳米孔隙，其中的微尺度效应使多组分气流变得更加复杂。本文采用格子Boltzmann方法模拟不同条件下二维微孔隙中的二组分页岩气流动。研究了双组分页岩气的孔隙尺度输运机制，详细讨论了页岩气流动的气体分离现象。发现页岩气中各组分的摩尔分数沿微孔分布不均匀，双组分压力驱动的页岩气流中存在气体分离现象。每个物种沿微孔的摩尔分数分布受压力驱动气流的克努森数、压力比、页岩气组成和每个物种的摩尔分数的影响。特别是，我们发现双组分页岩气沿微孔的摩尔分数分布和压力分布与压力比有关，与压力梯度无关。随着页岩气中 CH4 摩尔分数的增加，出口处的混合气速度和沿微孔的滑移速度都变大。克努森数和压力比都影响 CO2 注入过程中微孔中 CH4 CO2 混合物的 CO2 摩尔分数分布，而两者的影响相反。此外，没有外力的浓度扩散受微孔宽度和气体混合物之间的浓度差的影响。