Dynamics of immiscible three-phase flow in a mixed-wet Ketton limestone sample


  1. Dynamics of immiscible three-phase flow in a mixed-wet Ketton limestone sample>
    . Dynamics of displacement in mixed-wet porous media. EarthArXiv. .

    Abstract — We identify a distinct two-phase flow invasion pattern in a mixed-wet porous medium. Time-resolved high-resolution synchrotron X--ray imaging is used to study the invasion of water through a small rock sample filled with oil, characterized by a wide non-uniform distribution of local contact angles both above and below 90°. The water advances in a connected front, but throats are not invaded in decreasing order of size, as predicted by invasion percolation theory for uniformly hydrophobic systems. Instead, we observe pinning of the three-phase contact between the fluids and the solid, manifested as contact angle hysteresis, which prevents snap-off and interface retraction. In the absence of viscous dissipation, we use an energy balance to find an effective, thermodynamic, contact angle for displacement and show that this angle increases during the displacement. Displacement occurs when the local contact angles overcome the advancing contact angles at a pinned interface: it is wettability which controls the filling sequence. The product of the interfacial curvatures, the Gaussian curvature, is negative, implying well-connected phases which is consistent with pinning at the contact line while providing a topological explanation for the high displacement efficiencies in mixed-wet media.

  2. Dynamics of immiscible three-phase flow in a mixed-wet Ketton limestone sample>
    . In Situ Characterisation of Three-Phase Flow in Mixed-Wet Porous Media Using Synchrotron Imaging. Earth and Space Science Open Archive. .
    • https://doi.org/10.1002/essoar.10502988.1
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    Abstract — We use fast synchrotron X-ray imaging to understand three-phase flow in mixed-wet porous media to design either enhanced permeability or capillary trapping. The dynamics of these phenomena are of key importance in subsurface hydrology, carbon dioxide storage, oil recovery, food and drug manufacturing, and chemical reactors. We study the dynamics of a water-gas-water injection sequence in a mixed-wet carbonate rock. During the initial waterflooding, water displaced oil from pores of all size, indicating a mixed-wet system with local contact angles both above and below 90°. When gas was injected, gas displaced oil preferentially with negligible displacement of water. This behaviour is explained in terms of the gas pressure needed for invasion. Overall, gas behaved as the most non-wetting phase with oil the most wetting phase; however pores of all size were occupied by oil, water and gas, as a signature of mixed-wet media. Thick oil wetting layers were observed, which increased oil connectivity and facilitated its flow during gas injection. A chase waterflooding resulted in additional oil flow, while gas was trapped by oil and water. Furthermore, we quantified the evolution of the surface areas and both Gaussian and the total curvature, from which capillary pressure could be estimated. These quantities are related to the Minkowski functionals which quantify the degree of connectivity and trapping. The combination of water and gas injection, under mixed-wet immiscible conditions leads to both favourable oil flow, but also to significant trapping of gas, which is advantageous for storage applications.