Abstract:

Understanding the mechanism of fluid droplets attached to micro/nano channels being displaced by another fluid can shed light on the transport law in unconventional oil and gas development. The cross-scale nature of the process and the strong interaction between droplet and displacement fluid determine that a hybrid simulation method must be used. In previous researches, the commonly used interface conditions of adding an external force interfere with the transfer of shear stress from the continuous domain to the molecular domain, resulting in incorrect calculation of the flow resistance. A new method of arranging a virtual wall instead of adding a force was used to solve the problem of incorrect shear stress transfer. Based on this new method, the cases are compared where the droplets are monoatomic molecules and butane, and the cases that the wall is completely rigid and the wall particles are allowed to vibrate, respectively. The results show that the traditional method of adding a force could lead to errors up to 65% in the flow drag, while arranging a virtual wall could keep error within 1%, thus has significant advantage. The introduction of droplet molecular structure and the wall particle vibration both have a great influence on the flow resistance.

Key words: multiscale, microscale, molecular simulation, unconventional oil and gas

摘要：

理解微纳孔隙通道内驱替液对附着在壁面上的液滴进行驱替这一过程的机理，有助于深入了解非常规条件下油气开发过程中的输运规律。该过程的跨尺度特性以及液滴与驱替液之间的强烈相互作用，决定了必须使用混合模拟方法进行研究。然而在已有的研究中，通常采用的阻逸力界面条件干扰了连续区域到分子尺度区域的切应力传递，导致流动阻力计算不正确。采用布置虚拟壁面的新方法代替阻逸力界面条件，以解决切应力传递不正确的问题。在此基础上，比较了液滴分别为单原子分子和复杂流体的情形，以及壁面完全刚性和允许壁面粒子振动的情形。结果表明传统的阻逸力方法可导致流动阻力的误差高达65%，而采用虚拟壁面的界面条件可将误差降至1%以内，具有显著优势。此外，研究结果还显示液滴为复杂流体和允许壁面粒子振动均对流动阻力有较大的影响。

关键词: 多尺度, 微尺度, 分子模拟, 非常规油气