Abstract The interfacial tension (IFT) between oil and water impacts many industrial operations. For example, in low salinity flooding, water with optimal salinity is injected into an oil reservoir, to change the oil/water interfacial tension and fluid/rock interfacial energy to mobilize trapped oil and enhance the displacement of oil. Theoretical and experimental studies have shown that different ions can enhance or inhibit the production. To develop a fundamental understanding of IFT in these systems, particularly in the context of salinity and the ion-type effect, molecular dynamics simulations were used to probe the change in IFT with the salt types and concentrations. In agreement with experimental measurements, our results show that the oil/water IFT increases with increasing salt concentration, with the increase dependent on the salt species. The results revealed that the presence of divalent anions at the interface increases the electrostatic interactions, which leads to a smaller increase in the IFT compared to other salts. Moreover, the analysis showed that the increase in IFT is due to ion depletion near the interface. The water orientations at the interface and the bulk explain why this depletion occurs.

中文翻译：

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深入了解影响水/油界面张力作为盐类型和浓度函数的机制

摘要 油和水之间的界面张力 (IFT) 会影响许多工业操作。例如，在低矿化度驱油中，将最佳矿化度的水注入油藏，改变油水界面张力和流体/岩石界面能，以调动圈闭的油，增强油的驱替能力。理论和实验研究表明，不同的离子可以增强或抑制其产生。为了对这些系统中的 IFT 有一个基本的了解，特别是在盐度和离子型效应的背景下，分子动力学模拟被用来探测 IFT 随盐类和浓度的变化。与实验测量结果一致，我们的结果表明油/水 IFT 随着盐浓度的增加而增加，随着盐种类的增加而增加。结果表明，界面处二价阴离子的存在增加了静电相互作用，与其他盐相比，这导致 IFT 的增加较小。此外，分析表明 IFT 的增加是由于界面附近的离子消耗所致。界面和主体处的水方向解释了为什么会发生这种耗尽。