Abstract: The mass transfer by diffusion of CO₂ molecules between oil and aqueous phases is of great significance to the enhanced oil recovery by CO₂ flooding in tight reservoirs. Through combining experimental measurement data with theoretical diffusion model, this paper simultaneously determines the diffusion coefficients of CO₂ molecules in oil and aqueous phases in the carbonated water-crude oil binary system using the trial-and-error method. This study focuses on the influence of initial pressure of the oil-water mixing system on the diffusion coefficient, and deeply explores the variations of the density of oil-aqueous phases, CO₂ concentration, oil-water interface movement, and CO₂ diffusion front position in the oil phase during diffusion. The results show that:(1)As CO₂ diffuses from the aqueous phase into the oil phase, the pressure of the carbonated water-crude oil system increases. After 10 hours of diffusion at 60℃, the pressure is increased by 24% to 31% for the initial pressures of 15.39,19.25 and 22.82 MPa (Experiments 1 to 3). (2)Near the two-phase interface, the density of the aqueous phase and CO₂ concentration in the aqueous phase gradually decrease, while the density of the oil phase and CO₂ concentration in the oil phase gradually increases, causing the volume of the oil phase to expand and that of the aqueous phase to shrink, and the two-phase interface moves toward the aqueous phase. (3)The higher the initial pressure, the greater the diffusion coefficient. The CO₂ diffusion coefficient in the aqueous and oil phase in experiments 1 to 3 is increased by 52% and 9.2%, respectively, indicating that the CO₂ diffusion coefficient in the aqueous phase is more sensitive to the initial pressure. (4)The higher the initial pressure, the farther the CO₂ diffusion front migrates in the oil phase within the same time period. After 100 hours of diffusion, the migrating distances of the front positions in experiment 1 to 3 are 4.11 cm, 4.32 cm and 4.43 cm, respectively.

Key words: mass transfer by diffusion, tight oil, diffusion coefficient, trial-and-error method, diffusion front, interface characteristics

摘要： CO₂分子在油水相间的扩散传质行为对于致密油藏注CO₂提高采收率具有重要意义。通过融合实验测定数据和理论扩散模型，利用试错法同时确定了碳酸水-原油二元体系中CO₂分子在油、水两相中的扩散系数。重点研究了油水混合体系的初始压力对扩散系数的影响规律，深入探讨了扩散过程中油水相密度、CO₂浓度、油水界面移动以及CO₂在油相中扩散前缘位置的变化过程。研究结果表明：①随着CO₂从水相扩散进入油相，碳酸水-原油体系压力增大，60℃下，扩散10 h，初始压力分别为15.39 MPa、19.25 MPa和22.82 MPa（实验1—实验3）体系，压力增加24%~31%；②在两相界面附近，水相密度及水相中CO₂浓度逐渐降低，而油相密度及油相中的CO₂浓度逐渐升高，导致油相体积膨胀，水相体积收缩，两相界面向水相方向移动；③初始压力越高，扩散系数越大。实验1—实验3水相和油相中CO₂扩散系数的增幅分别为52.0%和9.2%，表明水相中CO₂扩散系数对初始压力更敏感；④初始压力越高，相同扩散时间内CO₂在油相中的扩散前缘运移越远，扩散100 h后，实验1—实验3前缘位置运移距离分别为4.11 cm、4.32 cm和4.43 cm。

关键词: 扩散传质, 致密油, 扩散系数, 试错法, 扩散前缘, 界面特征