Multiphase flow of supercritical CO~2~ (ScCO~2~) and water in porous media is central to a large range of applications in the energy and environmental sectors, such as enhanced oil recovery, groundwater remediation, and geologic CO~2~ storage and sequestration (CCS). Although these operations are almost always performed at large scales, it is now well-accepted that many macroscopic flow behaviors are controlled by physics down to the micrometer scale, that is flow within each individual pore of the porous medium. For instance, recent evidence highlighted the important role played by transient flow events called Haines jumps, which typically originate in one single pore and occurr on the time scale of milliseconds. It was shown that Haines jumps can greatly accelerate the flow near the fluid-fluid interfaces and render inertial effects critical, falsifying the assumption of low-Reynolds-number flow that is widely used in conventional models. Moreover, these so-called single-pore events (*i.e.*, tens of micrometers) were shown to extend their effects as far as a few millimeters, highlighting their non-locality. These effects may thus greatly affect the accuracy of predictive models if not properly accounted for. Additionally, wetting properties of the porous matrix, which are difficult to model numerically, pose a further control on the observed physics and dynamics, thus challenging its microscopic and macroscopic descriptions. Despite the importance of pore-scale flow processes, our understanding of the physics associated with them remains limited due to the inherent complexity of the multiphase flow in porous media and due to the lack of direct quantitative observations.

To this end, the pore-scale flow of water and CO~2~ is quantified using high-speed microscopic particle image velocimetry (micro-PIV) under reservoir-relevant conditions (80 bar, 21°C) in 2D circular microfluidic model porous media (called micromodels). The micromodels used in these experiments were fabricated from silicon and glass using microfabrication techniques, with the porous matrix formed with arrays of 2D poly-disperse cylinders mimicking a natural porous medium. The uniqueness of the micromodels is that they are of a circular shape, with the inlet at the center and the outlet at the outer edge. Circular micromodels (i.e., radial displacement of multiphase flow) are superior to rectangular ones (i.e., linear displacement) as the former can significantly mitigate the boundary effects that can arise in the later. The wettability of the internal surfaces of the micromodels were modified by the silanization technique when necessary. The high-speed micro-PIV measurements were achieved with the aid of a epi-fluorescence microscope, a high-speed laser and a high-speed camera, allowing us to achieve truly temporally- and spatially-resolved data, which is indispensable to advance our understanding of the dynamics of the flow at the pore-scale. Statistical analysis during both steady and transient flows is performed to gain further insight into the intermittent behaviors as well as to quantify the effects of wettability on such behaviors.

Preliminary results show that multiphase flow of CO~2~ and water in hydrophilic micromodels is strongly dominated by successive and pore-scale burst events, resulting velocities of two orders of magnitude larger than the bulk velocity. When the surface wettability was altered to near-wetting-neutral conditions, capillarity and instability are significantly suppressed, leading to more compact and axisymmetric displacement of water by CO~2~. In this scenario, flow velocities are generally small, but higher velocities are induced by merging of adjacent interfaces, revealing a new mechanism of pore space invasion.


Quantifying the Dynamics of Water-CO2 Multiphase Flow in Microfluidic Porous Media Using High-Speed Micro-PIV

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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