Browsing by Author "Xiao, Siyang"

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    Destabilization, Propagation, and Generation of Surfactant-Stabilized Foam during Crude Oil Displacement in Heterogeneous Model Porous Media
    (American Chemical Society, 2018) Xiao, Siyang; Zeng, Yongchao; Vavra, Eric D.; He, Peng; Puerto, Maura; Hirasaki, George J.; Biswal, Sibani L.
    Foam flooding in porous media is of increasing interest due to its numerous applications such as enhanced oil recovery, aquifer remediation, and hydraulic fracturing. However, the mechanisms of oil-foam interactions have yet to be fully understood at the pore level. Here, we present three characteristic zones identified in experiments involving the displacement of crude oil from model porous media via surfactant-stabilized foam, and we describe a series of pore-level dynamics in these zones which were not observed in experiments involving paraffin oil. In the displacement front zone, foam coalesces upon initial contact with crude oil, which is known to destabilize the liquid lamellae of the foam. Directly upstream, a transition zone occurs where surface wettability is altered from oil-wet to water-wet. After this transition takes place, a strong foam bank zone exists where foam is generated within the porous media. We visualized each zone using a microfluidic platform, and we discuss the unique physicochemical phenomena that define each zone. In our analysis, we also provide an updated mechanistic understanding of the "smart rheology" of foam which builds upon simple "phase separation" observations in the literature.
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    Microfluidic Devices for Characterizing Pore-scale Event Processes in Porous Media for Oil Recovery Applications
    (Journal of Visualized Experiments, 2018) Vavra, Eric D.; Zeng, Yongchao; Xiao, Siyang; Hirasaki, George J.; Biswal, Sibani L.
    Microfluidic devices are versatile tools for studying transport processes at a microscopic scale. A demand exists for microfluidic devices that are resistant to low molecular-weight oil components, unlike traditional polydimethylsiloxane (PDMS) devices. Here, we demonstrate a facile method for making a device with this property, and we use the product of this protocol for examining the pore-scale mechanisms by which foam recovers crude oil. A pattern is first designed using computer-aided design (CAD) software and printed on a transparency with a high-resolution printer. This pattern is then transferred to a photoresist via a lithography procedure. PDMS is cast on the pattern, cured in an oven, and removed to obtain a mold. A thiol-ene crosslinking polymer, commonly used as an optical adhesive (OA), is then poured onto the mold and cured under UV light. The PDMS mold is peeled away from the optical adhesive cast. A glass substrate is then prepared, and the two halves of the device are bonded together. Optical adhesive-based devices are more robust than traditional PDMS microfluidic devices. The epoxy structure is resistant to swelling by many organic solvents, which opens new possibilities for experiments involving light organic liquids. Additionally, the surface wettability behavior of these devices is more stable than that of PDMS. The construction of optical adhesive microfluidic devices is simple, yet requires incrementally more effort than the making of PDMS-based devices. Also, though optical adhesive devices are stable in organic liquids, they may exhibit reduced bond-strength after a long time. Optical adhesive microfluidic devices can be made in geometries that act as 2-D micromodels for porous media. These devices are applied in the study of oil displacement to improve our understanding of the pore-scale mechanisms involved in enhanced oil recovery and aquifer remediation.
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    Visualization of Crude Oil Displacement by Foam Enhanced Oil Recovery (EOR) in Microfluidic Devices
    (2016-04-22) Xiao, Siyang; Biswal, Sibani
    Foam flooding, as an enhanced oil recovery (EOR) process, has become of great interest to the oil industry. However, the mechanism of oil displacement by foam has not been fully understood. This thesis describes the visualization of foam on a pore-scale level using microfluidic devices. A micro model patterned with a heterogeneous porous media was designed to mimic reservoir with permeability contrast. The micro model is made with Norland Optical Adhesive 81 (NOA81), an optical transparent material with high organic resistance available for crude oil tests. Foam was injected into the reservoir micro model to displace trapped crude oil. The smart rheology of foam can help mitigate reservoir heterogeneity by separating into dry- and wet-phases such that the flow resistance in high-perm region is much higher than that in low-perm region. Bubbles could block the high-perm region and divert more fluids to displace the oil in low-perm part. One hypothesis is that the phase separation of foam is due to the difference in capillary entry pressure. Thusly foam shows a better sweep efficiency compared to gas and water flooding. This thesis also compared different injection foam quality for different surfactant solutions. Results showed that higher foam quality has better sweep efficiency, especially in low-perm region. This is because high foam quality can create denser lamellae that increase flow resistance, which will thusly divert more liquid phase into low-perm region, improving oil displacement. Foam made with mixture of Lauryl Betaine (LB) and C14-16 Alpha Olefin Sulfonate (AOS) showed a better sweep compared to foam consisting of only AOS. The reason is that AOS foam tended to collapse more easily, changing to very coarse foam.