Abstract:

Nanofluid flooding technology can effectively improve unconventional oil recovery, of which microscopic mechanism needs to be further investigation. In this paper, the effects of Reynolds number (Re), type of nanoparticles (NPs), concentration of nanoparticles, lipophilicity/lipophobic and surface microstructure of rock stratums on oil displacement efficiency were analyzed by molecular dynamics (MD) method. The analysis of quantum chemical calculations and weak interactions showed that the intermolecular interactions increased with increasing molecular polarity index (MPI). Crude oil molecules were easily displaced by incoming flow at high MPI values, while crude oil molecules were easily adsorbed by rock stratums at low MPI values. Also, the attractive interactions between the oil droplets and the gold plates were more obvious without additional oil displacement agent. According to the total interactions, the oil displacement efficiency was the higher under the conditions of larger Re, CAAL, higher CAAL concentration, stronger rock stratum lipophobic and smaller rock stratum surface defect. The results of this work will be potentially valuable for improving the oil displacement technology, enhancing the oil displacement efficiency and improving the quality of produced crude oil.

Key words: nanoparticles, microscale, multiphase flow, oil displacement, molecular dynamics, fluid dynamics

摘要：

纳米流体驱油技术能有效提高非常规石油开采效率，但其潜在的微观机理仍需进一步探究。本文采用分子动力学（MD）方法，从分子间总相互作用的角度分析了雷诺数（Re）、纳米颗粒（NPs）类型、纳米颗粒浓度、岩层亲/疏油性和岩层表面微结构对驱油效率的影响。量子化学计算和弱相互作用分析结果表明，分子极性指数（MPI）越高，分子间相互作用越强。原油分子的MPI越高，越容易被来流驱替；原油分子的MPI越低，越容易吸附于岩层。另外，在无外加驱油剂的情况下，油滴与金板间的吸引作用更加明显。根据总相互作用可知，当Re越大、采用纳米颗粒CAAL（3条羧酸链和3条烷烃链修饰的SiO₂）的浓度越大、岩层的疏油性越强和岩层表面凹陷越小时，油滴与岩层之间的相互作用越小，驱油效率越高。本文对改进现有驱油技术、提高驱油效率以及改善采出原油品质具有重要的指导意义。

关键词: 纳米粒子, 微尺度, 多相流, 驱油, 分子动力学, 流体动力学