Methane scattering on porous kerogen surfaces and its impact on mesopore transport in shale
Methane scattering on porous kerogen surfaces and its impact on mesopore transport in shale
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DOI：
10.1016/j.fuel.2022.123259
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发表时间：
2022-05
期刊：
影响因子：
7.4
通讯作者：
Yichong Chen;Jun Li;S. Datta;Stephanie Y. Docherty;L. Gibelli;M. Borg
中科院分区：
文献类型：
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作者：
Yichong Chen;Jun Li;S. Datta;Stephanie Y. Docherty;L. Gibelli;M. Borg
揭示气体分子在多孔表面上的散射行为对于为描述页岩储层中气体动力学的动力学输运模型开发准确的边界条件至关重要。在这里，我们使用高保真分子动力学模拟来解决甲烷分子和现实的有机干酪根表面之间的气体-表面相互作用，并评估广泛使用的散射内核的适用性。我们的研究结果表明，紧密的矩阵孔隙度有一个可以忽略不计的影响的时间尺度和长度尺度的散射过程，这可以被认为是瞬时的时间和局部的空间。虽然反射速度分布显示，常见的麦克斯韦，Cercignani-Lampis和Yamamoto散射模型未能完全捕捉到的散射细节的甲烷干酪根，特别是当入射分子速度高，麦克斯韦模型预测最好的反射角光束图案和整体反射速度分布的粗糙干酪根表面。然而，对于低速撞击，页岩应用的更多特征，所有散射模型给出类似的速度分布，这是由观察到的高度气体表面调节驱动的。我们发现，一个麦克斯韦模型与校准的切向动量调节系数，其中接近统一的表面粗糙度增加到1.2纳米，是足以重现可比的速度分布和质量流率内适度限制干酪根中孔。麦克斯韦模型和我们的分子模拟之间的偏差只观察到高度稀薄的运输问题，但这种稀薄超出了页岩储层的应用领域。因此，本文报道了多孔和粗糙的干酪根表面的第一次散射研究，并证明了麦克斯韦模型的适用性，它可以很容易地纳入气体动力学求解器预测的表观渗透率的页岩中孔和大孔网络。
Revealing the scattering behaviour of gas molecules on porous surfaces is essential to develop accurate boundary conditions for kinetic transport models that describe the gas dynamics in shale reservoirs. Here, we use high-fidelity molecular dynamics simulations to resolve the gas–surface interactions between methane molecules and realistic organic kerogen surfaces, and to assess the applicability of the widely used scattering kernels. Our results show that the tight matrix porosities have a negligible effect on the timescale and lengthscale of the scattering process, which can be considered instantaneous in time and local in space. Although reflected velocity distributions reveal that the common Maxwell, Cercignani–Lampis and Yamamoto scattering models fail to fully capture the scattering details of methane on kerogen, especially when the incident molecular speeds are high, the Maxwell model predicts best the reflected angular beam pattern and the overall reflected velocity distribution for rough kerogen surfaces. However, for low-speed impingement, more characteristic of shale applications, all scattering models give similar velocity distributions, which are driven by the high degree of gas–surface accommodation observed. We find that a Maxwell model with a calibrated tangential momentum accommodation coefficient, which approaches unity as the surface roughness increases to∼ 2 nm, is enough to reproduce comparable velocity profiles and mass flow rates inside moderately confined kerogen mesopores. Deviations between the Maxwell model and our molecular simulations are only observed for highly rarefied transport problems, but this rarefaction lies beyond the realm of shale reservoir applications. This paper, therefore, reports the first scattering study on porous and rough kerogen surfaces, and demonstrates the applicability of the Maxwell model, which can be readily incorporated into gas kinetic solvers to predict the apparent permeability of shale with mesopore and macropore networks.