Abstract: Wettability is a key factor governing the distribution and migration behavior of formation fluids in oil and gas reservoirs, and a thorough understanding of its influence on CO₂-oil two-phase flow mechanisms is of great significance for enhancing tight oil and gas recovery and optimizing carbon sequestration technologies. However, existing studies predominantly relies on the assumption of uniform wettability assumption, failing to adequately capture the complex effects of heterogeneous wettability in real reservoirs. To address this gap, this study, based on the inherent heterogeneity of wettability in natural rocks, constructs a homogeneous porous medium model with randomly distributed wettability. Using computational fluid dynamics (CFD) methods, the microcosmic CO₂-oil flow processes are systematically simulated under varying CO₂ injection velocities, viscosity ratios, and interfacial tension conditions, with the aim of elucidating the effects of heterogeneous wettability on two-phase microscopic seepage characteristics, CO₂ displacement efficiency, and carbon sequestration performance. The results indicate that:(1) Compared with the single-wettability model, the fingering pathways formed during oil displacement by CO₂ flooding are highly correlated with the heterogeneous wettability distribution in porous media, and the oil recovery falls between those obtained in strongly CO₂-wet and strongly oil-wet systems. (2) A moderate increase in injection velocity enhances the dominance of viscous forces, enabling the flow to overcome local capillary resistance induced by wettability heterogeneity. This effectively suppresses capillary fingering, thereby improving sweep efficiency and increasing CO₂ storage capacity. (3) Viscosity-enhanced CO₂ effectively suppresses interfacial instability by reducing the viscosity contrast between the two phases, thereby improving flow continuity and sweep efficiency, and mitigating the effects of heterogeneous wettability. (4) The influence of heterogeneous wettability progressively weakens with decreasing interfacial tension. Under ultra-low interfacial tension conditions, although fluid snap-off is intensified, the sharp reduction in capillary resistance still results in enhanced displacement efficiency during CO₂ flooding. Overall, this study elucidates the mechanisms by which operational parameters regulate multiphase flow behavior under heterogeneous wettability conditions, and provides theoretical guidance and technical support for applications in multiphase flow, CCUS-EOR, and CO₂ fracturing.

Key words: heterogeneous wettability, CO₂ microscopic flow, CO₂ displacement and sequestration, computational fluid dynamics, fingering

摘要： 润湿性是影响油气藏中地层流体分布和运移特征的关键因素,深入理解其对CO₂-油两相流动机制的作用对于提升致密油气开采效率及优化碳封存技术具有重要意义。但现有研究多基于均匀润湿假设,未充分考虑真实储层中非均匀润湿性的复杂影响。鉴于此,基于真实岩石非均匀润湿的特性,构建了润湿性随机分布的均质多孔介质模型,并采用计算流体力学方法,系统模拟不同CO₂注入速度、黏度比和界面张力条件下的CO₂-油微观流动过程,探讨非均匀润湿性对两相微观渗流特征、CO₂驱油效率及碳封存性能的影响,揭示了在非均匀润湿性影响下施工参数对多相渗流的调控机制。研究表明:①与单一润湿性模型相比,CO₂驱替油相时形成的指进路径与多孔介质的非均匀润湿性分布高度相关,油相采收率介于强亲CO₂和强亲油模型之间;②适当提高注入速度增强了黏滞力主导作用,促使流动突破非均匀润湿性产生的局部毛细管阻力,有效抑制毛细管指进现象,从而提升波及效率与CO₂封存量;③增稠CO₂通过缩 小两相黏度差异,有效抑制界面不稳定性,提高流动连续性和波及面积,降低非均匀润湿性的影响;④非均匀润湿性影响随界面张力降低而减弱,在超低界面张力下,流体"卡断"加剧,但因毛细管阻力骤降,CO₂驱油效率仍会提高。

关键词: 非均匀润湿性, CO₂微观流动, CO₂驱油与封存, 计算流体力学, 指进