Microfluidic studies of fluid-fluid interaction and multiphase flow in fractures and channels
Keywords: Energy Resources Engineering.

World energy demand increases as global population increases. Seeking new solutions and improving the current energy systems are two attractive options to address the existing problems. Processes of interest include CO$_{2}$ storage security, hydrogen storage, and enhanced oil recovery. Studying fluid behavior at pore scale, improves understanding of fundamental mechanisms and enables mechanistic control of the processes involved. Multiphase and multi-component fluid flow is dictated and controlled by pore-scale phenomena. Understanding fluid-fluid interactions and multiphase flow behavior in complex porous media is the essential component of optimizing the subsurface energy design. Microfluidic devices with representative geometry, and length scales are essential to delineate the fundamental mechanisms dictating the pore-scale fluid behavior of multiphase flow in fractures and channels. Therefore, a primary objective of this research is to develop cutting-edge microfluidic devices. My research improves mechanical and physical characteristics of transport processes in micromodels through development of new microfluidic devices, thorough experimental frameworks, and computer-assisted techniques to process and model the results. First, we designed and fabricated a new microfluidic device to better enable study of foam microstructure and rheology in planar fractures. The workflow included finite element analysis of several designs to enhance the pressure tolerance of the device. The new design illustrated improved ability to sustain large differential pressure compared to previous designs in the literature. Our findings validated the previous microvisual studies mentioned in the literature and revealed that foam apparent viscosity is a strong function of foam quality and water velocity at small qualities and this dependency decreases for greater foam qualities and water velocities. Second, we investigated foam flow behavior in microscale fractures and developed a mechanistic transient foam flow model using the population balance method. Microscale experiments in fractures with apertures of 25 and 88 $\mu m$ were used to validate the model for pressure drop, gas saturation, and bubble texture. Key differences related to modeling foam in fractures are the potential for continuously varying gas-liquid curvature in fractures and the relationship of this curvature to apparent foam viscosity. Incorporation of a local foam flow resistance factor is important to representing flow physics accurately. Third, we designed and fabricated a new microfluidic device with a meter-long channel and a rectangular cross section to study the flow behavior of long gas bubbles in noncircular-cross-section capillaries. Our calculations of channel curvature, Dean number, and centripetal acceleration for this novel symmetric loop design illustrated that this capillary tube on a chip behaves, essentially, as a straight channel for a wide range of velocity, U. We found that the pressure drop experienced by bubbles varies as $Ca^{2/3}$ over the range