Study of colloidal transport and multiphase flow in bead-based micromodels with surface charge and wettability heterogeneities

Abstract

Micromodels are porous media analogs that help scientists understand the transport phenomena in real-world porous media at the laboratory scale. Compared with traditional field- and column-scale experiments, micromodels have two distinct advantages: (1) its transparency allows researchers to directly visualize relevant transport phenomena occurred inside through optical microscopy. (2) its highly controllable physicochemical properties allow scientists to conveniently decouple the porous medium parameters from various process parameters and study their specific or synergistic impacts systematically. In this thesis we developed new approaches to fabricate bead-based micromodels to study the pore-scale and population behavior of colloidal transport and multiphase flow through porous media. By injecting microscopic beads with different surface functionalities in a microfluidic channel, we were able to fabricate unconsolidated porous media analogs with surface charge and wettability heterogeneities. We also developed a MATLAB program that detected the mass center of each bead in the porous media, which allowed us to replicate the exact experimental domains in numerical simulators for faithful comparison between experiments and modelling. For colloidal transport in porous media with surface charge heterogeneity, we performed experiments at the single pore level and directly extracted the deposition coefficient between colloidal particles and the bead collectors under the favorable deposition conditions. Meanwhile we also obtained the surface blocking function of the particle deposition. Both information can be used directly in numerical simulations, thus eliminating the need of fitting parameters. We obtained a good agreement in the deposition coefficient between pore-scale and population experiments. We further used Norland Optical Adhesive 81 (NOA81) as the material to fabricate micromodels with heterogeneous wettability. Due to its high elastic modulus NOA81 can sustain high pressure during multiphase flow. Our preliminary experiments for the displacement of oil by water demonstrated the feasibility of studying multiphase flow in a close-packed porous medium with wettability heterogeneities.