Abstract
In the past few years, micromodels have become a useful tool for visualizing flow phenomena in porous media with pore structures, e.g., the multifluid dynamics in soils or rocks with fractures in natural geomaterials. Micromodels fabricated using glass or silicon substrates incur high material cost; in particular, the microfabrication-facility cost for making a glass or silicon-based micromold is usually high. This may be an obstacle for researchers investigating the two-phase-flow behavior of porous media. A rigid thermoplastic material is a preferable polymer material for microfluidic models because of its high resistance to infiltration and deformation. In this study, cyclic olefin copolymer (COC) was selected as the substrate for the micromodel because of its excellent chemical, optical, and mechanical properties. A delicate micromodel with a complex pore geometry that represents a two-dimensional (2D) cross-section profile of a fractured rock in a natural oil or groundwater reservoir was developed for two-phase-flow experiments. Using an optical visualization system, we visualized the flow behavior in the micromodel during the processes of imbibition and drainage. The results show that the flow resistance in the main channel (fracture) with a large radius was higher than that in the surrounding area with small pore channels when the injection or extraction rates were low. When we increased the flow rates, the extraction efficiency of the water and oil in the mainstream channel (fracture) did not increase monotonically because of the complex two-phase-flow dynamics. These findings provide a new mechanism of residual trapping in porous media.
Highlights
When applying engineering processes to porous media involving two-phase flows, e.g., enhanced oil recovery, geological carbon sequestration, water infiltration, and groundwater remediation, a fractured pore structure is commonly observed
We demonstrate the use of cyclic olefin copolymer (COC), a thermoplastic material, in geo-fluid experimental micromodel investigations
We performed the experiments in micromodels comprising mainstream channels different widths and different injection and extraction rates
Summary
When applying engineering processes to porous media involving two-phase flows, e.g., enhanced oil recovery, geological carbon sequestration, water infiltration, and groundwater remediation, a fractured pore structure is commonly observed. Some irregular patterns that have properties similar to real porous media have been generated using the Delaunay triangulation [10] Such patterns can be designed for studying flow behaviors in pore geometries that are present either in natural porous materials or in theoretical models [1,3,11]. The material cost and, in particular, the microfabrication-facility cost for making a glass or silicon-based micromodel are high; this creates obstacles for researchers investigating two-phase-flow behavior in porous media. We fabricate an artificial pore structure via hot embossing and use UV/Ozone for bonding as well as for controlling surface wettability. We perform two-phase-flow micromodel experiments in a fractured pattern and investigate the spatial distribution of oil and groundwater subjected to injection and extraction rates
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