Construction and validation of microfluidic platforms for investigation of multiphase flow and nanofluids in porous media
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Flow and transport in porous media is the fundamental physical process in many important applications such as hydrocarbon recovery, carbon dioxide subsurface sequestration, treatment of non-aqueous liquid pollutions in soil systems, and flooding control for fuel cell systems. Clear description, correct modeling and precise prediction of flow in porous media are of great significance. Although many single-phase and multiphase systems can be characterized using macroscopic models such as Darcy’s law (or the multiphase form of it), other complex flow systems, such as emulsion flow, nanoparticle suspension flow, etc., require a more detailed description. For those complex cases, revealing the pore-scale physics is necessary for larger-scale modeling and predictions. Microfluidics provide a simple way to visualize micron-scale flow behavior with excellent controllability, thus helping to clarify the fundamental pore-scale flow mechanisms and is, therefore, useful for studying flow and transport in porous media. In this work, several special micromodel designs from the single-pore level to pore-network level on microchips were made in order to capture realistic pore-scale flow mechanisms while keeping the system simplified enough for easy quantification. At the single-pore level, the trapping and mobilization of a non-wetting oil droplet at a pore-throat structure are investigated on an ideal pore-throat microfluidic geometry. A simple physical model is derived and the effects of bare nanoparticle aqueous suspension in mobilizing oil is further studied. A dual-permeability microchannel is used to study the emulsion flow in natural fracture system and a synergistic effect between nanoparticles and non-ionic surfactant is investigated to stabilize the emulsion and to potentially improve sweep efficiency. At the pore-network-pore level, a 2.5-D porous micromodel is fabricated to introduce essential 3-D feature in traditional 2-D porous micromodel. On this advanced 2.5-D micromodel, multiple complex fluid systems, including spontaneous imbibition, unstable water drainage, ultra-low IFT flooding, bubble evolution under Ostwald ripening, nanofluid flooding, etc., have been studied, with new physics revealed and modeled. A novel EOR method using nanoparticle treated oil (NPTO) is proposed and validated.