Direct Investigations of Multiphase Flow Phenomena in Microfluidic Models

Résumé du livre

As global energy requirements continue to rise, greater demand is being placed on oil producers to maximize production from conventional reservoirs. Conventional oil production techniques leave behind a significant amount of oil due to discontinuities in the oil phase, causing oil trapping. A primary driver of this phenomenon is snap-off. Understanding of how snap-off is affected by straight walled pore-throat geometries is limited. Better understanding of how geometry mediates snap-off is necessary for more accurate and precise simulations of flow through complex porous media. An idealized three dimensional microfluidic device was used to create an approximate replica of simulated pore-throat systems. The platform allows for the studies of the effect of throat aspect ratio upon displacement mechanisms in a water and oil system to be directly investigated. Three dimensional pore-throat geometries were produced with increasing aspect ratio to investigate the Rayleigh-Plateau instability in free standing bridges of nonwetting liquid. The system was designed to be as close to perfectly water-wet as possible while maintaining regions to allow corner flow and wetting phase continuity. This study was performed with the intent of forming an accurate model of how geometry influences snap-off events. It is hypothesized that liquid will become columnated in the throat and will form a free standing bridge between pores. At this point the bridge either remains stable or deteriorates, depending on whether or not the throat aspect ratio exceeds the Rayleigh-Plateau instability criteria. Experimental results indicated fundamental shortcomings in the fabrication medium, which motivated the development of a new high tensile strength silicone for experimental platforms and fabrication intermediates. Mechanical testing was performed on the high tensile strength silicones, verifying anecdotal strength observations. High tensile strength silicone allows for greater flexibility in the fabrication of complex and high aspect ratio structures. Demonstrating the utility of this material, novel triangular channels machined into glass substrates were replicated using the high tensile strength silicone. Triangular channels provide an excellent representation for naturally occurring porous media undergoing multiphase flow by creating superior wetting phase flow and continuity by increasing the relative wetting phase cross-sectional area. Triangular channels also provide superior capillary pressure control inside a microfluidic device for applications sensitive to capillary pressures. Capillary pressure measurements were performed within triangular channels, verifying that they provide an acceptable microfluidic platform for multiphase flow studies with results consistent with those predicted theoretically. The work performed indicates that snap-off is affected by to throat aspect ratios and length, but other factors such as mixed wettability seem to play a crucial role. To fully investigate the phenomena, microfluidic devices with better wettability will be required. The full development and implementation of triangular channels fabricated in glass will provide devices with the improved geometry, optical, and wettability characteristics for multiphase flow studies.