In this study, we summarize and discuss the data reported from a series of multiscale experiments to explore the interactions of salinity and aqueous ions at fluid/fluid and rock/fluid interfaces and to understand the pore-scale oil-recovery mechanisms in controlled-ionic-composition waterflooding (CICW). Experimental data on various crude-oil/brine/carbonate and crude oil/brine physicochemical changes/effects at elevated temperatures were obtained using a variety of static and dynamic techniques at different scales ranging through atomic/molecular/macroscopic scales. The techniques include surface-force apparatus (SFA), cryo-broad-ion-beam scanning electron microscope (BIB-SEM), zeta-potentials, microscope-based oil liberation, macroscopic contact angles, interfacial shear rheology, and integrated thin-film drainage apparatus (ITFDA). The salinities of brines were varied from zero-salinity deionized (DI) water to higher-salinity injection water in addition to changing the individual ion compositions.

The integration of results obtained from different multiscale experiments showed that both salinity and individual aqueous ions play a major role not only in determining the oil release from the rock surface owing to the interactions at the rock/fluid interface but also in impacting released oil-ganglion dynamics for efficient oil mobilization through the interactions at the fluid/fluid interface. The key findings can be summarized as follows: (1) at zero salinity, unfavorably much higher adhesion and stronger rigid films to adversely impact crude-oil-droplet coalescence were observed at rock/fluid and fluid/fluid interfaces, respectively; (2) an optimal lower salinity containing a sufficient amount of sulfate ions is necessary to cause nanoscale ion exchange at the rock/fluid interface that changes the surface charge/potential to favorably alter adhesion and microscopic contact angles for efficient oil release from the rock surface; and (3) an adequate salinity containing higher amounts of magnesium and calcium ions is desired to form less-rigid films at the fluid/fluid interface that promote the coalescence of released oil ganglia for effective mobilization. On the basis of these novel findings, controlled-ionic-composition water can be defined as a tailored water containing certain salinity and selective composition of three key ions including: sulfates, magnesium, and calcium. It must contain lower amounts of monovalent ions and should have the right balance of the three key ions to enable favorable interactions at both fluid/fluid and rock/fluid interfaces in carbonates. The novelty of this work is that it systematically analyzes and consolidates all the multiscale (atomic/molecular/macroscopic scales) experimental data obtained using rock and crude-oil samples from the same carbonate reservoir. Also, consistent trends were identified from different experimental techniques at both rock/fluid and fluid/fluid interfaces to establish a clear connection among multiscales and subsequently understand the causative pore-scale mechanisms responsible for oil recovery in CICW processes. In other words, this work has successfully transmitted the physics behind individual mechanisms and their interplay through different length scales to directly address one of the key open questions raised by Bartels et al. (2019).

The analysis on multiscale aqueous-ion interactions at the two interfaces performed in this study resulted in the major finding that the controlled-ionic-composition water effect in carbonates is a combination of two effects, one being related to the release of oil attached on rock surfaces (wettability change) and the other being related to improved oil-phase connectivity and better oil mobilization (enhanced coalescence of oil ganglia). It also highlighted the important learning point that not every low-salinity water can become a controlled-ionic-composition water for carbonates. These new learnings and the novel knowledge gained provide useful practical guidelines on how to design optimal injection-water chemistries for waterflooding projects in carbonate reservoirs.

在这项研究中，我们总结并讨论了一系列多尺度实验报告的数据，以探索盐度和含水离子在流体/流体和岩石/流体界面的相互作用，并了解受控离子中的孔隙尺度的油采收机理。组合注水（CICW）。使用各种静态和动态技术，通过原子/分子/宏观尺度在不同尺度上获得了各种原油/盐水/碳酸盐以及原油/盐水在高温下的物理化学变化/效应的实验数据。这些技术包括表面力设备（SFA），低温宽离子束扫描电子显微镜（BIB-SEM），ζ电位，基于显微镜的油释放，宏观接触角，界面剪切流变学和集成薄膜排水设备（ITFDA）。

从不同的多尺度实验获得的结果的综合表明，由于岩石/流体界面的相互作用，盐度和各个水离子不仅在确定岩石表面的油释放中起主要作用，而且还影响着释放的油神经节通过流体/流体界面上的相互作用实现有效油动员的动力学。主要发现可归纳为：（1）在盐度为零时，分别在岩石/流体和流体/流体界面处观察到不利的高附着力和较强的刚性膜，对原油-液滴的聚结产生不利影响；（2）包含足够数量的硫酸根离子的最佳较低盐度是引起岩石/流体界面处纳米级离子交换所必需的，从而改变表面电荷/电势以有利地改变附着力和微观接触角，从而有效地从岩石表面释放油; （3）需要含有较高量的镁和钙离子的足够的盐度，以在流体/流体界面形成较少刚性的膜，从而促进释放的油神经节的聚结以有效地动员。基于这些新发现，可将受控离子组成的水定义为含有一定盐度和选择性组成的三个关键离子（包括硫酸盐，镁和钙）的定制水。它必须包含较少量的一价离子，并应具有三个关键离子的正确平衡，以使碳酸盐中的流体/流体界面和岩石/流体界面都具有良好的相互作用。这项工作的新颖之处在于它系统地分析和合并了使用同一碳酸盐岩储层中的岩石和原油样本获得的所有多尺度（原子/分子/宏观尺度）实验数据。同样，从岩石/流体和流体/流体界面的不同实验技术中发现了一致的趋势，从而在多尺度之间建立了清晰的联系，并随后理解了引起CICW过程中石油采收的致孔尺度机制。换一种说法，这项工作成功地通过不同的长度尺度传递了各个机制及其相互作用之间的物理原理，从而直接解决了Bartels等提出的关键的开放性问题之一。（2019）。

这项研究对两个界面上的多尺度水离子相互作用进行了分析，得出的主要发现是碳酸盐中的受控离子组成水效应是两种效应的组合，其中一种与岩石上附着的油的释放有关表面（可湿性变化），另一个与改善的油相连通性和更好的油动员（增强的​​油性神经节聚结）有关。它还强调了重要的学习要点，即并非每种低盐度水都可以成为碳酸盐的受控离子组成水。这些新的学习成果和获得的新颖知识为如何设计碳酸盐岩储层注水项目的最佳注入水化学方法提供了有用的实用指导。