The mixed-wet nature of reservoir formations imposes a wide range of rock wettability from strong resident-fluid wetting to strong invading-fluid wetting. The characteristics of two-phase flow in porous media composed of mixed-wetting surfaces remain poorly understood. In this study, we investigated the displacement of resident ethylene glycol (EG) by hexane in two mixed-wet micromodels of identical 2.5-D geometry heterogeneity, with uniformly or heterogeneously distributed patches strongly wetting to hexane. These patches are mixed among pores with unaltered EG-wetting surfaces. Along with control tests in the originally EG-wet micromodel, we show the classic fingering and transitions in flow regimes at (capillary number) from −7.2 to −3.9. Moreover, pore-scale distributions of wettability and their spatial correlation influence displacement efficiency. In the two mixed-wet micromodels, we found (a) an increase of steady-state hexane saturation at the end of experiments by up to 0.12 in the capillary fingering regime and a decrease of at most by 0.06 in the viscous fingering regime, compared to the EG-wet micromodel, and (b) dispersed and fragmented hexane distribution after displacement. Brine drainage during supercritical CO₂ (scCO₂) injections in these micromodels occurs with lower wettability contrasts, and under similar viscosity ratios and interfacial tensions resulted in higher displacement efficiency relative to displacement of EG by hexane. While mixed-wettability can enhance displacement efficiency compared to uniform wettability, the dynamics of immiscible fluids in strong mixed-wet reservoirs are expected to be less pronounced in contributing to the efficiency of geological CO₂ sequestration, oil recovery, and remediation of hydrocarbon-contaminated aquifers.

中文翻译：

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孔隙网络尺度润湿性异质性对不混溶流体位移的影响：微模型研究

储集层的混合润湿性质对岩石的润湿性施加了广泛的影响，从强驻留流体润湿到强侵入流体润湿。由混合润湿表面组成的多孔介质中的两相流特征仍然知之甚少。在这项研究中，我们研究了在两个具有相同 2.5-D 几何异质性的混合湿微模型中，己烷对常驻乙二醇 (EG) 的置换，均匀或不均匀分布的斑块对己烷具有很强的润湿性。这些贴片混合在具有未改变的 EG 润湿表面的孔中。随着原始 EG 湿微模型中的控制测试，我们展示了流态的经典指法和转变（毛细管数）从 -7.2 到 -3.9。此外，润湿性的孔隙尺度分布及其空间相关性影响驱替效率。在两个混合湿微模型中，我们发现 (a) 在实验结束时，在毛细管指法中稳态己烷饱和度增加了 0.12，在粘性指法中最多减少了 0.06，相比之下到 EG 湿微模型，以及（b）置换后分散和破碎的己烷分布。超临界 CO ₂ (scCO ₂) 在这些微模型中注入的润湿性对比度较低，并且在相似的粘度比和界面张力下，相对于用己烷置换 EG 而言，置换效率更高。虽然与均匀润湿性相比，混合润湿性可以提高驱替效率，但预计强混合润湿性油藏中不混溶流体的动力学在促进地质 CO ₂封存、采油和修复烃污染方面的作用不那么明显。含水层。