The Impact of Wettability and Surface Roughness on Fluid Displacement and Capillary Trapping in 2‐D and 3‐D Porous Media: 1. Wettability‐Controlled Phase Transition of Trapping Efficiency in Glass Beads Packs

Helmut Geistlinger,Bilal Zulfiqar

doi:10.1029/2019wr026826

Helmut Geistlinger, Bilal Zulfiqar

Open Access

https://doi.org/10.1029/2019wr026826

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Abstract

AbstractFluid invasion, displacement of one fluid by another in porous media, is important in a large number of industrial and natural processes. Of special interest is the trapping of gas and oil clusters. We study the impact of wettability on fluid pattern formation and capillary trapping in three‐dimensional glass beads packs (dmean = 1 mm) during fluid invasion at capillary numbers of 10−7 using μ‐CT. The invading fluid was water, and the defending fluid was air. The contact angle of the glass beads was altered between 5° and 115° using Piranha cleaning and silanization. We analyzed the front morphology of the invading fluid, the residual gas saturation, the fluid occupation frequency of pores, and the morphology and statistics of the trapped gas clusters. We found a sharp transition (crossover) at a critical contact angle θc = 96°. Below θc the morphology of the displacement front was flat and compact caused by the strong smoothing effect of cooperative filling. Above θc the morphology of the displacement front was fractal and ramified caused by single bursts (Haines jumps). Across this dynamical phase transition the trapping efficiency changes from no trapping to maximal trapping. For θ > θc the experimental results show that invasion percolation governs the fluid displacement. Strong indicators are the universal scaling behavior of the size distribution of large clusters (relative data error εdata < 1%) and their linear surface‐volume relationship (R2 = 0.99).

Highlights

Capillary trapping of gas clusters, residual NAPL clusters, and oil ganglia plays a central role in many natural and technological processes
We study the impact of wettability on fluid pattern formation and capillary trapping in three‐dimensional glass beads packs during fluid invasion at capillary numbers of 10−7 using μ‐CT
We analyze the front morphology of the invading fluid (Figure 7), the residual gas saturation (Figure 8), the occupation frequency (Figure 9), and the morphology and statistics of the trapped clusters (Figures 10 and 11)

Summary

Introduction

Capillary trapping of gas clusters, residual NAPL clusters, and oil ganglia plays a central role in many natural and technological processes. Most of the displacement processes are slow (quasistatic), and viscous forces can be neglected, that is, capillary numbers Ca are smaller than 10−6 In their pioneering work, Chatzis et al (1982) conducted a comprehensive study on residual oil trapping using different porous media (glass beads packs [GBS], sandstones, and 2‐D micromodels [MMs]). They discussed different trapping mechanisms in different porous media and developed a clear physical picture for the two main trapping mechanisms by instructive examples: (i) Bypass trapping is visualized by pore doublets, and (ii) snap‐off trapping (capillary instability) is visualized by an undulating capillary with high pore‐throat aspect ratio. Their experimental results demonstrated the effect of pore structure, topology, and heterogeneity on capillary trapping

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