Stabilizing Fluid-Fluid Displacements in Porous Media Through Wettability Alteration

Mathias Trojer, Michael L. Szulczewski, and Ruben Juanes

Phys. Rev. Applied 3, 054008 – Published 21 May 2015

Abstract

We study experimentally how wettability impacts fluid-fluid-displacement patterns in granular media. We inject a low-viscosity fluid (air) into a thin bed of glass beads initially saturated with a more-viscous fluid (a water-glycerol mixture). Chemical treatment of glass surfaces allows us to control the wetting properties of the medium and modify the contact angle $θ$ from 5° (drainage) to 120° (imbibition). We demonstrate that wettability exerts a powerful influence on the invasion morphology of unfavorable mobility displacements: increasing $θ$ stabilizes fluid invasion into the granular pack at all capillary numbers. In particular, we report the striking observation of a stable radial displacement at low capillary numbers, whose origin lies on the cooperative nature of fluid invasion at the pore scale.

Received 10 September 2014

DOI:https://doi.org/10.1103/PhysRevApplied.3.054008

Authors & Affiliations

Mathias Trojer, Michael L. Szulczewski, and Ruben Juanes^*

Massachusetts Institute of Technology, 77 Massachusetts Avenue, Building 1, Cambridge, Massachusetts 02139, USA

^*juanes@mit.edu

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Vol. 3, Iss. 5 — May 2015

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Images

Figure 1
Experimental setup: a thin glass bead pack (nominal bead-size diameter $\bar{d} \approx 490 μ m$ ) of height $b$ of 5–7 beads is confined in between the bottom and top lid of a radial Hele-Shaw cell of radius $R = 10.6 cm$ (a confinement weight $w = 18 kg$ rests on top of the lid). Air is injected from the top at a fixed rate $Q$ to displace a water-glycerol mixture that fills the cell initially. Time-lapse images are taken with a camera placed underneath the cell.
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Figure 2
Visual phase diagram of the fluid-fluid-displacement morphologies obtained during air injection (dark) into a porous medium filled with a mixture of water and glycerol (clear), as a function of the effective capillary number ${Ca}^{*}$ [Eq. (1)] and the static contact angle $θ$ ranging from strict drainage ( $θ \approx 5 °$ ) to forced imbibition ( $θ \approx 120 °$ ). The viscosity contrast between the fluids is $M = η_{liq} / η_{air} \approx 320$ .
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Figure 3
(a) Fractal dimension $D_{f}$ vs static contact angle $θ$ for all single-frame snapshots presented in Fig. 2, computed using the box-counting method. (b) Average finger width $\bar{w}$ vs radial distance $r$ , for ${Ca}^{*} = 50$ and all different contact angles. (c) Effective finger width $\bar{\bar{w}}$ vs static contact angle $θ$ in the viscous-fingering regime ( ${Ca}^{*} = 5$ and 50); the monotonically increasing trend confirms quantitatively the stabilizing effect of wetting to the invading fluid. Inset: schematic illustrating the computation of the average finger width $\bar{w}$ at any given radial distance $r$ .
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Figure 4
(a) Bead-size distribution of MO-SCI GL0191B4/425-600SC soda-lime spheres used to create the solid porous matrix; the measured mean average bead-size diameter of 200 representative individual spherical beads is $\bar{d} = 488 μ m$ . (b) Regular square lattice initially placed in the circular hole cut to maintain reproducibility of bead-pack height $b$ , porosity, and permeability of individual experiments.
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Figure 5
Wettability alteration on soda-lime glass using chemical vapor deposition (CVD). The silanization procedure is tuned to achieve the desired wetting properties for five different contact angles with respect to the viscous water-glycerol mixture and air: (1) $θ = 5 ° \pm 1.2 °$ , $O_{2}$ plasma asher; (2) $θ = 20 ° \pm 0.8 °$ , no CVD treatment; (3) $θ = 62 ° \pm 1.8 °$ , dichlordimethylsilan, 5% in a vacuum oven at $150 ° C$ ; (4) $θ = 89 \pm 0.8 °$ , dichlordimethylsilan, 5%; (5) $θ = 121 \pm 2.3 °$ , (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-trichlorosilane.
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Physical Review Applied