Event-based contact angle measurements inside porous media using time-resolved micro-computed tomography

Arjen Mascini,Veerle Cnudde,Tom Bultreys

doi:10.1016/j.jcis.2020.03.099

Arjen Mascini, Veerle Cnudde + Show 1 more

Open Access

https://doi.org/10.1016/j.jcis.2020.03.099

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Abstract

HypothesisCapillary-dominated multiphase flow in porous materials is strongly affected by the pore walls’ wettability. Recent micro-computed tomography (mCT) studies found unexpectedly wide contact angle distributions measured on static fluid distributions inside the pores. We hypothesize that analysis on time-resolved mCT data of fluid invasion events may be more directly relevant to the fluid dynamics. ExperimentWe approximated receding contact angles locally in time and space on time-resolved mCT datasets of drainage in a glass bead pack and a limestone. Whenever a meniscus suddenly entered one or more pores, geometric and thermodynamically consistent contact angles in the surrounding pores were measured in the time step just prior to the displacement event. We introduced a new force-based contact angle, defined to recover the measured capillary pressure in the invaded pore throat prior to interface movement. FindingsUnlike the classical method, the new geometric and force-based contact angles followed plausible, narrower distributions and were mutually consistent. We were unable to obtain credible results with the thermodynamically consistent method, likely because of sensitivity to common imaging artifacts and neglecting dissipation. Time-resolved mCT analysis can yield a more appropriate wettability characterization for pore scale models, despite the need to further reduce image analysis uncertainties.

Highlights

Multiphase flow in porous materials is crucial for e.g. safe subsurface CO2 storage [1], groundwater remediation [2] and efficient⇑ Corresponding author.PEM fuel cells [3,4]
We introduce a new force-based receding contact angle definition derived from the measured curvature of a fluid meniscus which triggers it to move through a pore throat
This work aims to improve our understanding of wettability by calculating receding contact angles for individual pore-filling events, rather than for a static fluid distribution as a whole

Summary

Introduction

PEM fuel cells [3,4]. This process is strongly affected by the porous medium’s wettability: its affinity to be in contact with one fluid over another [5]. The wettability, typically expressed as a contact angle between the solid and the fluids, induces capillary forces which exert a strong influence on fluid displacement [6]. Drainage is the displacement of a wetting fluid by a non-wetting fluid, while the reverse process is called imbibition [7].

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