Abstract

Understanding fluid dynamics is essential for various applications, including subsurface energy storage and recovery, fluid flow management, and environmental sustainability. However, the complexity of subsurface geological systems poses significant challenges to the effectiveness of reservoir engineering processes. Mixed wettability, commonly observed in natural formations like carbonate and shale rocks, adds an extra layer of complexity to multiphase flow dynamics, making fluid behavior difficult to predict. Its impact remains poorly understood due to the inherent challenges of in-situ characterization and experimental replication of these conditions.

This dissertation presents a novel framework for studying multiphase fluid flow in mixed-wettability environments using innovative microfluidic systems that mimic natural rock conditions. A pioneering methodology was developed to fabricate mixed-wettability micromodels by combining photolithography with molecular vapor deposition (MVD), enabling precise spatial control of wettability at the pore scale. Advanced characterization methods, including contact angle measurements, X-ray photoelectron spectroscopy, and transmission electron, scanning electron, and atomic force microscopies, validated the robustness, reproducibility, and long-term stability of the technique, addressing the critical need for reliable platforms to study fluid flow in heterogeneous wetting environments.

Using these micromodels, the dissertation systematically explores the influence of mixed wettability on two-phase fluid displacement dynamics. Experimental observations revealed unique fluid behaviors, including meniscus transitions, preferential flow paths, and localized fluid trapping, driven by wettability contrasts. For the first time, pore-throat sizes were correlated with hydrophilic regions in rock-like microfluidic chips, enabling detailed analysis of wettability distribution and its effect on flow efficiency. Mixed-wettability configurations exhibited distinct flow dynamics, such as reduced injection times, enhanced sweep efficiencies, and non-monotonic saturation behaviors, highlighting the critical role of wettability heterogeneity in shaping fluid displacement and recovery efficiency.

Numerical simulations using Navier-Stokes equations and phase-field techniques complemented the experiments, accurately replicating fluid dynamics and providing a robust framework for scaling findings to complex geometries and reservoir conditions. By integrating cutting-edge fabrication techniques with experimental and numerical approaches, this dissertation advances pore-scale multiphase flow research, offering critical insights for subsurface energy applications, including enhanced oil recovery, carbon dioxide sequestration, and groundwater management.