Wettability Stabilizes Fluid Invasion into Porous Media via Nonlocal, Cooperative Pore Filling

Abstract

We study the impact of the wetting properties on the immiscible displacement of a viscous fluid in disordered porous media. We present a novel pore-scale model that captures wettability and dynamic effects, including the spatiotemporal nonlocality associated with interface readjustments. Our simulations show that increasing the wettability of the invading fluid (the contact angle) promotes cooperative pore filling that stabilizes the invasion, and that this effect is suppressed as the flow rate increases, due to viscous instabilities. We use scaling analysis to derive two dimensionless numbers that predict the mode of displacement. By elucidating the underlying mechanisms, we explain classical yet intriguing experimental observations. These insights could be used to improve technologies such as hydraulic fracturing, CO2 geo-sequestration, and microfluidics. 47.56.+r, Fluid-fluid displacement in porous media is important in natural and industrial processes at various scales, from enhanced energy recovery, CO 2 geo-sequestration, groundwater contamination and soil wetting and drying, to dyeing of paper or textiles and microfluidics. Fluid displacement is governed by the interplay between quenched disorder, short-range cooperative effects and long-range pressure screening, which depends on a large number of parameters, including the wettability-the relative affinity of the fluids to the solid. Consequently, the displacement patterns can range from a stable, compact front to highly ramified with preferential flow paths (fingers) [1]. Fluid invasion is a member of a broad class of problems characterized by competitive domain growth and nonlinear interface dynamics, including magnetic domains, biological films and flame front propagation [2]. The interface evolution in these systems is often modeled as a competition between the energy associated with the interaction between phases and constraints arising from disorder; the relative importance of the two can be tuned by properties such as wettability in fluid displacement or local random interaction fields in magnetic domains [3]. Understanding the impact of wettability on fluid invasion-the topic of this Letter-is therefore relevant to a wide range of phenomena of scientific and technological importance.Immiscible displacement can be classified according to the wettability into drainage or nonwetting invasion, where the displaced fluid preferentially wets the solid (contact angle θ < 90 • , measured through the defending fluid), or imbibition of a wetting fluid (θ > 90 • ). Intensive research has provided basic understanding of drainage, identifying different invasion behaviors and explaining their dependence on the flow velocity, fluid viscosities, interfacial tension, and the degree of porescale disorder ([4-7] and the references therein). Increasing θ was found to stabilize the displacement and reduce trapping in forced and gravity-driven drainage experiments [8,9].In contrast, relatively few works have studied imbibition, mostly for the stable case of a more vis...

Wettability control on multiphase flow in patterned microfluidics

“…Specifically, the morphology of the displacement pattern broadens as the invading fluid becomes more wetting to the medium. This observation was confirmed by recent experiments (20) and pore-scale simulations (21), which found that increasing the medium's affinity to the invading fluid makes the invasion pattern more compact at all Ca. However, the complete range of wetting conditions in imbibition is yet to be fully explored, especially in the regime where the invading fluid is strongly wetting to the porous medium.…”

Effects of Pore-Scale Disorder on Fluid Displacement in Partially-Wettable Porous Media

“…For high disorder ( λ  = 0.82), we reproduce the transition from CF to VF as the rate increases in drainage8 (wetting angle θ  < 90°, θ measured through the defending fluid, see Fig. 1c), and the smoothing (“stabilizing”) effect of increasing θ towards imbibition ( θ  > 90°), reducing trapping1112 (Fig. 2).…”

“…Increasing affinity of the invading fluid (from drainage to imbibition, when the invading fluid is more wetting) smoothes the invasion front, even at high, unfavorable M 10. At low rates, increasing wettability leads to a transition between CF and CO, whereas increasing Ca enhances viscous instabilities promoting VF, regardless of wettability1112. We note that the frequent use of the term “(in)stability” to describe the pattern, and the interchange of “stability” with “efficiency” or “compactness”.…”

Generalized three-dimensional lattice Boltzmann color-gradient method for immiscible two-phase pore-scale imbibition and drainage in porous media

“…This is an expected result; indeed in imbibition the invading fingers are expected to be broader [96][97][98], since they have the tendency to wet the pores and thus explore more easily neighboring pores. Figure 17 shows depth saturation profiles for both imbibition and drainage experiments in the viscous fingering regime.…”