Continuum to rarefied diffusive tortuosity factors in porous media from X-ray microtomography

Clogging constitutes a major operational issue for treatment wetlands. The rest period is a key feature of French Vertical Flow (VF) treatment wetlands and serves to mitigate clogging. An ex-situ drying experiment was performed to mimic the rest period and record structural changes in the porous media using X-ray Computed Tomography (CT). Samples containing the deposit and gravel layers of a first stage French VF treatment wetland were extracted and left to dry in a control environment. Based on CT scans, three phases were identified (voids, biosolids, and gravels). The impact of the rest period was assessed by means of different pore-scale variables. Ultimately, the volume of biosolids had reduced to 58% of its initial value, the deposit layer thickness dropped to 68% of its initial value, and the void/biosolid specific surface area ratio increased from a minimum value of 1.1 to a maximum of 4.2. Cracks greater than 3 mm developed at the uppermost part of the deposit layer, while, in the gravel layer, the rise in void volume corresponds to pores smaller than 2 mm in diameter. Lastly, the air-filled microporosity is estimated to have increased by 0.11 v/v.

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Imaging and Resistivity Studies of Saturation Gradients in Two-Phase Flow in 3-D Porous Media

MRS Proceedings ◽

10.1557/proc-464-371 ◽

1996 ◽

Vol 464 ◽

Cited By ~ 1

Author(s):

E. H. Kawamoto ◽

Po-Zen Wong

Keyword(s):

Computed Tomography ◽

Porous Media ◽

Two Phase Flow ◽

Water Saturation ◽

Glass Beads ◽

Water Phase ◽

Phase Flow ◽

Two Phase ◽

Vertical Column ◽

X Ray

ABSTRACTWe have carried out x-ray radiography and computed tomography (CT) to study two-phase flow in 3-D porous media. Air-brine displacement was imaged for drainage and imbibition experiments in a vertical column of glass beads. By correlating water saturation Sw with resistance R, we find that there is a threshold saturation S* ≈ 0.2, above which R(SW) ∼ Sw−2, in agreement with the empirical Archie relation. This holds true for both drainage and imbibition with littlehysteresis, provided that Sw remains above S*. Should Sw drop below S* during drainage, R(Sw) rises above the Archie prediction, exhibiting strong hysteresis upon reimbibition. This behavior suggests a transition in the connectivity of the water phase near S*, possibly due to percolation effects.

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Direct Numerical Simulation of Pore-Scale Trapping Events During Capillary-Dominated Two-Phase Flow in Porous Media

Transport in Porous Media ◽

10.1007/s11242-021-01619-w ◽

2021 ◽

Author(s):

Mosayeb Shams ◽

Kamaljit Singh ◽

Branko Bijeljic ◽

Martin J. Blunt

Keyword(s):

Numerical Simulation ◽

Porous Media ◽

Direct Numerical Simulation ◽

Complex Geometry ◽

Flow In Porous Media ◽

Pore Scale ◽

Contact Lines ◽

Two Phase ◽

X Ray ◽

Aspect Ratios

AbstractThis study focuses on direct numerical simulation of imbibition, displacement of the non-wetting phase by the wetting phase, through water-wet carbonate rocks. We simulate multiphase flow in a limestone and compare our results with high-resolution synchrotron X-ray images of displacement previously published in the literature by Singh et al. (Sci Rep 7:5192, 2017). We use the results to interpret the observed displacement events that cannot be described using conventional metrics such as pore-to-throat aspect ratio. We show that the complex geometry of porous media can dictate a curvature balance that prevents snap-off from happening in spite of favourable large aspect ratios. We also show that pinned fluid-fluid-solid contact lines can lead to snap-off of small ganglia on pore walls; we propose that this pinning is caused by sub-resolution roughness on scales of less than a micron. Our numerical results show that even in water-wet porous media, we need to allow pinned contacts in place to reproduce experimental results.

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