Characterizing the trapped phase in porous media is essential for many engineering applications, such as enhanced oil recovery, nuclear storage, and geological sequestration of CO₂. This study aims to study the distribution, evolution, and influencing factors of the remaining oil in the process of water flooding at the pore scale. The single-connected pore space model was established by reconstructing the real micron CT scanned images of carbonate rocks. The VOF (volume of fluid) method using FSF (filtered surface force) formulation was adopted on OpenFOAM platform to simulate the oil-water two-phase flow process at the pore scale. Different wettability and capillary number were considered in the model. The accuracy of the model was proved by comparing with previous experimental results. The results showed that in the process of water flooding, the complex pore structure would lead to the generation of remaining oil, and the phase circulation phenomenon can be observed in the remaining oil and presents two distribution forms: co-current driven flow and lid-cavity driven flow. It also revealed that the phase recirculation increases the viscous dissipation. Further research also showed that the two forms of recirculation could be transferred by changing the wettability and that a higher capillary number was more beneficial for reducing the remaining oil saturation.

表征多孔介质中的困相对于许多工程应用至关重要，例如提高石油采收率、核储存和 CO _{2 的}地质封存. 本研究旨在从孔隙尺度研究水驱过程中剩余油的分布、演化及影响因素。通过重建碳酸盐岩真实微米CT扫描图像，建立单连通孔隙空间模型。OpenFOAM平台采用采用FSF（过滤表面力）公式的VOF（流体体积）方法模拟孔隙尺度的油水两相流动过程。模型中考虑了不同的润湿性和毛细管数。通过与前人实验结果的对比，证明了模型的准确性。结果表明，在水驱过程中，复杂的孔隙结构会导致剩余油的产生，在剩余油中可观察到相循环现象，呈现两种分布形式：并流驱动流和盖腔驱动流。它还揭示了相再循环增加了粘性耗散。进一步研究还表明，两种再循环形式可以通过改变润湿性进行转移，较高的毛细管数更有利于降低剩余油饱和度。