CO₂ huff-n-puff is one of the most important methods to enhanced oil recovery, which can simultaneously improve oil production and achieve CO₂ geological storage. Due to the fluctuation of formation pressure, water-oil-CO₂ three phase migration in porous structures was affected significantly by supercritical CO₂ exsolution and expansion. However, the existing research on phase distribution is not enough to understand the mechanism of three-phase migration and the essential processes beneath the phase distribution are still not clear. Here, we developed a high-temperature and high-pressure micro-PIV (Particle Image Velocimetry) and fluorescence visualization experimental system (10 MPa, 50°C), which realized the simultaneous measurement of the velocity field and phase distribution of the water-oil-CO₂ three-phase. The multiphase migration process under different wettability conditions during the supercritical-subcritical CO₂ exsolution were captured. The results showed that the exsolution induced CO₂ bubbles expansion in aqueous and oil phase blocked the preferential migration passage and dominated different multiphase migration mechanisms under different wettability. It was found that in water-wet condition, the aqueous phase can still migrate downstream through the water film between the CO₂/oil and the wall, unable to further drive CO₂/oil downstream. While in oil-wet condition, the aqueous phase eventually broke through the oil phase blocked at throats and formed a new preferential migration passage, pushing part of the oil phase encapsulating CO₂ bubbles downstream. Our research reveals the multiphase migration mechanism beneath the phase distribution under different wettability during the exsolution process of the huff-n-puff, which provides a new insight for CO₂ enhanced oil recovery and geological storage.

CO ₂吞吐是提高石油采收率的最重要方法之一，它可以同时提高石油产量和实现CO ₂地质封存。由于地层压力波动，超临界CO ₂对多孔结构中水-油-CO ₂三相运移的影响显着解离和扩张。然而，现有的相分布研究还不足以理解三相迁移的机理，相分布之下的基本过程仍不清楚。在这里，我们开发了高温高压微PIV（粒子图像测速）和荧光可视化实验系统（10 MPa，50°C），实现了水的速度场和相分布的同时测量-油-CO ₂三相。捕获了超临界-亚临界CO ₂溶出过程中不同润湿性条件下的多相迁移过程。结果表明，溶出诱导 CO ₂水相和油相中气泡的膨胀阻断了优先迁移通道，在不同润湿性下主导了不同的多相迁移机制。发现在水湿条件下，水相仍可通过CO ₂ /油与壁之间的水膜向下游迁移，无法进一步驱使CO ₂ /油向下游移动。而在油湿状态下，水相最终冲破喉部阻塞的油相，形成新的优先运移通道，推动部分油相包裹CO ₂下游泡沫。我们的研究揭示了huff-n-puff出溶过程中不同润湿性下相分布下的多相迁移机制，为CO ₂提高石油采收率和地质封存提供了新的思路。