Fabrication technique for mixed hydrophobic–hydrophilic wettability micromodels: Experimental and numerical validation

Subsurface reservoirs often display heterogeneous hydrophobic–hydrophilic wettability, known as mixed wettability, which significantly impacts the behavior of multiphase fluid flow and their entrapments. Microfluidic systems have emerged as a crucial tool for studying the impact of wettability on fluid flow at the pore scale. However, creating microfluidic devices with controlled spatial distribution of mixed wettability has been a challenge. This study investigates a novel technique for fabricating micromodels with controlled mixed wettability, using photolithography and molecular vapor deposition of perfluorodecyltrichlorosilane. The primary objective is to validate this technique through two-phase flow experiments and numerical simulations. Six different configurations of mixed wettability micromodels, including single channels with horizontal and vertical mixed wettability, Y-shaped channels with two and multiple mixed-wet branches, and mixed-wet pore-doublet models, were designed and fabricated to mimic the complex wettability variations found in natural porous media. Experimental observations, captured with a high-resolution microscope and high-speed camera, provided dynamic insights into the influence of mixed wettability on two-phase fluid flow. Pore-scale simulations, conducted using the phase-field approach in COMSOL Multiphysics®, were performed to replicate and validate the experimental findings. Simulations showed excellent agreement with the experimental results, affirming the effectiveness of the proposed fabrication technique, the robustness of the experimental setup, and the reliability of the numerical model.