There are several key factors proposed in the literature responsible for oil mobilization and recovery by nanofluids as enhanced oil recovery agents. These factors include interfacial tension (IFT) reduction, wettability alteration, inhibition of fines migration, and flow profile control. However, there is not a general consensus on the relative contribution and importance of each factor. Moreover, very little pore-scale evidence for the role of these mechanisms in a natural porous medium is available, especially for carbonate rocks. To fill the gaps, we directly studied mechanisms leading to oil mobilization by SiOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiO}_\mathrm{{x}}$$\end{document}- and Al2O3-based nanofluids at the pore-scale. A set of spontaneous imbibition tests was performed in both Berea sandstone and Fond-du-Lac dolomite samples. Three-dimensional high-resolution fluid occupancy maps were captured using an X-ray micro-CT scanner, and in-situ contact angle distributions were obtained at different locations directly from the X-ray images. We found that wettability reversal rather than IFT reduction was the main pore-scale mechanism for oil recovery using simple nanofluids (without other chemical additives). Furthermore, in Berea, there was a synergistic effect between the non-ionic surfactant and SiOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiO}_\mathrm{{x}}$$\end{document} nanoparticles for enhancing oil recovery through both IFT reduction (due to surfactant) and wettability reversal (due to nanoparticles). A set of statistical analyses of the trapped oil ganglia in Berea shows that the surfactant-augmented SiOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiO}_\mathrm{{x}}$$\end{document} nanofluid generated smaller oil ganglia, which further proves that nanofluid can assist in oil mobilization.

中文翻译：

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天然多孔介质中纳米流体诱导的润湿性梯度和吸收增强：孔隙尺度实验研究

文献中提出了几个关键因素，负责通过纳米流体作为提高石油采收率剂的石油动员和采收。这些因素包括界面张力 (IFT) 降低、润湿性改变、细粉迁移的抑制和流动剖面控制。然而，对于每个因素的相对贡献和重要性尚未达成普遍共识。此外，关于这些机制在天然多孔介质中的作用的孔隙尺度证据非常少，特别是对于碳酸盐岩。为了填补空白，我们通过 SiOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage 直接研究了导致石油动员的机制{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiO}_\mathrm{{x}}$$\end{document}- 和基于 Al2O3 的纳米流体在孔隙处-规模。在 Berea 砂岩和 Fond-du-Lac 白云岩样品中进行了一组自吸测试。使用 X 射线显微 CT 扫描仪捕获三维高分辨率流体占用图，并直接从 X 射线图像中获得不同位置的原位接触角分布。我们发现润湿性逆转而不是 IFT 降低是使用简单纳米流体（无其他化学添加剂）采油的主要孔隙尺度机制。此外，在 Berea 中，非离子表面活性剂与 SiOx\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy } \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\hbox {SiO}_\mathrm{{x}}$$\end{document} 纳米粒子用于通过 IFT 减少（由于表面活性剂）和润湿性逆转（由于纳米粒子）来提高石油采收率。