Microfluidic studies of fluid-fluid interaction and multiphase flow in fractures and channels

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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 $10^{-7} < Ca < 10^{-4}$ where $Ca = \frac{\mu U}{ \sigma}$. Thus, the drag also scales as $Ca^{2/3}$, or equivalently with liquid flow rate as $Q^{2/3}$ confirming previous predictions. Fourth, we used our microchannel to explore the effect of surfactant and nanoparticles on the gas-liquid interface. Our interfacial tension experiments showed that addition of surfactant and nanoparticles enhanced the stability of the interface by reducing the interfacial tension. The pressure drop versus capillary number behavior proved that this relation is only affected by the interfacial tension between the phases, even for nanoparticle solutions. Hence, after normalizing pressure gradient with respect to interfacial properties the drag scales as $Ca^{2/3}$ over the range $10^{-7} < Ca < 10^{-2}$. Fifth, we investigated fluid interactions and scrutinized the development of microscopic mixing as fluids flow through microchannels. Experimental testing and computational fluid dynamics were used to study such phenomena and explore possible relationships between the rate of injection and the development of miscibility. Additional testing variables included viscosity, the presence of obstacles, and the pattern of obstacles. The results of this study were used to construct a quantitative model to explain the miscibility behavior between different fluids. Finally, mechanistic understanding of pore-level behavior set the basis for upscaling and informing the design of optimal injection fluids at the field scale. Combining previous learning experiences, we developed field-scale models to study fluid behavior at reservoir scales. To do this, we developed a field-scale simulator to investigate the effect of fracture configurations on foam flow behavior and propagation. Additionally, we developed and implemented a smooth framework to study the sensitivity of foam flow behavior in porous media. Our analysis showed that increasing foam quality results in decreasing bubble texture and consequently, decreasing the pressure gradient. This result occurs due to decreased bubble generation and increased bubble coalescence due to gas diffusion. However, analyzing the effect of initial water saturation on pressure gradient, water saturation, and bubble texture on the model revealed that, increasing the initial water saturation postpones the foam breakthrough significantly.


Type of resource text
Form electronic resource; remote; computer; online resource
Extent 1 online resource.
Place California
Place [Stanford, California]
Publisher [Stanford University]
Copyright date 2022; ©2022
Publication date 2022; 2022
Issuance monographic
Language English


Author Nazari, Negar
Degree supervisor Kovscek, Anthony R. (Anthony Robert)
Thesis advisor Kovscek, Anthony R. (Anthony Robert)
Thesis advisor Horne, Roland N
Thesis advisor Tartakovsky, Daniel
Degree committee member Horne, Roland N
Degree committee member Tartakovsky, Daniel
Associated with Stanford University, Department of Energy Resources Engineering


Genre Theses
Genre Text

Bibliographic information

Statement of responsibility Negar Nazari.
Note Submitted to the Department of Energy Resources Engineering.
Thesis Thesis Ph.D. Stanford University 2022.
Location https://purl.stanford.edu/wv723gx4929

Access conditions

© 2022 by Negar Nazari
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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