Imaging and characterizing fluid invasion in micro-3D printed porous devices with variable surface wettability.

Fluid invasion in porous media widely exists in many applications, such as waterflooded oil/gas recovery, carbon geo-sequestration, water filtration and membrane distillation. The invasion dynamics is significantly affected by the surface wettability, interfacial tension, pore-throat topology and many other parameters. In this work, we experimentally investigate the effect of surface wettability on the multiphase flow behavior, particularly the interfacial dynamics, through direct visualization of fluid invasion in a porous microfluidic device (micromodel). The micromodels have been fabricated by using a micro-stereolithography 3D printer with acrylate-based resins. With a high printing resolution of up to 2 μm, these micromodels successfully mimic the complex pore-throat features of natural porous media (i.e. rocks) based on their thin-section or micro-CT images. Moreover, the transparency of the as-printed micromodel also enables microfluidic flow imaging. By injecting different fluids into surface-modified micromodels, we observe and study the invasion dynamics, including the lateral interfacial curvature, multiphase flow path and fluid trapping behavior, under various surface wettability conditions. By combining optical flow imaging and numerical simulation, we have systematically analyzed the wettability-dependent residue distribution and revealed four different types of trapping mechanisms. This work offers a novel methodology to study microscale flow in porous media with micro-3D printing and multiphase flow imaging.