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The simultaneous flow of multiple fluids through a porous medium is important to several earth science applications, such as underground gas storage and groundwater remediation. The intricate interplay between capillary, viscous and gravitational forces inside heterogeneous pore geometries gives rise to non-linear and complex flow dynamics. Even though it is known that imbibition comprises capillary fluctuations which are nonlocal in nature, the temporal and spatial structure of these remain unclear. This is because it was until recently impossible to directly measure unsteady 3D fluid velocity fields in (opaque) porous media.
Recent breakthroughs in 3D X-ray particle tracking velocimetry (Tom Bultreys et al., 2022, 2024) have made it possible to directly measure pore-scale flow dynamics. Here, we use this methodology to investigate imbibition for the first time. We investigate the impact of viscosity ratio at low capillary numbers on unsteady velocity fields during imbibition. To do this, sub-second micro-CT images are acquired at the TOMCAT beamline at the Swiss Light Source while withdrawing the nonwetting fluid from the pore space at a constant, slow flow rate. The nonwetting fluid contains silver-coated hollow glass tracers which are tracked to measure the velocity fields. This enables us to probe the underlying flow dynamics during snap-offs, investigate the effects of interfacial drag on the nonwetting fluid and study ganglia remobilization dynamics. We find that during imbibition displacements, acceleration occurs along tortuous pathways, spanning almost the entire connected oil cluster. Sections of these pathways are then reactivated when the next displacement occurs. When the viscosity ratio is near or less than one, frictional drag along the interface results in recirculation within the nonwetting fluid, similar to what has been seen in micromodel experiments (Roman et al., 2019; Zarikos et al., 2018).
These results are the first pore-scale velocimetry measurements of imbibition in 3D opaque porous materials. These findings inform on the viscous-capillary force balance during imbibition. This will aid in better constraining the time and length scales of energy fluctuations during imbibition, which bears importance to recent theories of energy-dynamics based upscaling (McClure et al., 2021, 2022).
| References | Bultreys, Tom, Van Offenwert, S., Goethals, W., Boone, M. N., Aelterman, J., & Cnudde, V. (2022). X-ray tomographic micro-particle velocimetry in porous media. Physics of Fluids, 34(4), 42008. https://doi.org/10.1063/5.0088000 Bultreys, Tom, Ellman, S., Schlepütz, C. M., Boone, M. N., Pakkaner, G. K., Wang, S., et al. (2024). 4D microvelocimetry reveals multiphase flow field perturbations in porous media. Proceedings of the National Academy of Sciences, 121(12). https://doi.org/10.1073/pnas.2316723121 McClure, J. E., Berg, S., & Armstrong, R. T. (2021). Capillary fluctuations and energy dynamics for flow in porous media. Physics of Fluids, 33(083323), 1–16. https://doi.org/10.1063/5.0057428 McClure, J. E., Fan, M., Berg, S., Armstrong, R. T., Berg, C. F., Li, Z., & Ramstad, T. (2022). Relative permeability as a stationary process: Energy fluctuations in immiscible displacement. Physics of Fluids, 34(9), 092011. https://doi.org/10.1063/5.0107149 Roman, S., Soulaine, C., & Kovscek, A. R. (2019). Pore-scale visualization and characterization of viscous dissipation in porous media. Journal of Colloid and Interface Science, 558, 269–279. https://doi.org/10.1016/j.jcis.2019.09.072 Zarikos, I., Terzis, A., Hassanizadeh, S. M., & Weigand, B. (2018). Velocity distributions in trapped and mobilized non-wetting phase ganglia in porous media. Scientific Reports, 8(1). https://doi.org/10.1038/s41598-018-31639-4 |
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| Country | Belgium |
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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