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

Abstract

Fluid 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 (d mean = 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 θ c = 96°. Below θ c the morphology of the displacement front was flat and compact caused by the strong smoothing effect of cooperative filling. Above θ c 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 > θ c 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 ε data < 1%) and their linear surface-volume relationship (R 2 = 0.99).

The Impact of Wettability and Surface Roughness on Fluid Displacement and Capillary Trapping in 2‐D and 3‐D Porous Media: 2. Combined Effect of Wettability, Surface Roughness, and Pore Space Structure on Trapping Efficiency in Sand Packs and Micromodels

“…Contact angle dependency of the trapping efficiency for (a) 1 mm sand, and for (b) 1 mm glass beads (Geistlinger & Zulfiqar, 2020). (a) The yellow marked area shows the region of snap‐off trapping caused by precursor TFF.…”

“…The experimental procedure for wettability alteration, experimental setup, and methodology follows the same protocols described in Part 1 (Geistlinger & Zulfiqar, 2020). We studied NS with different wettability: NS1: strongly water wet ( θ = 5°), NS2: weakly water wet ( θ = 33°), NS3–5: intermediate wet ( θ = 81°, 88°, 99°), and NS6: weakly air wet ( θ = 115°).…”

“…Hence, the fluid meniscus can be reasonably resolved by 22 voxels along the diameter. Image processing was carried out according to the protocol described in Part 1 of the study (Geistlinger & Zulfiqar, 2020).…”

“…Figure 1c in Jung Our counter example MM4-Si shows that depending on the pore space structure a fractal displacement front is possible. Hence, this smoothing effect that is intensively discussed and studied experimentally and numerically in literature (see references in Geistlinger & Zulfiqar, 2020) is connected to artificial porous media, which exhibit a smooth surface, a high porosity (0.6-0.85), and ideal circular grains.…”

“…In Geistlinger and Zulfiqar (2020), we studied the impact of wettability on fluid pattern formation and capillary trapping in 3‐D glass bead packs during fluid invasion at a capillary number of 10 −7 using μ ‐CT. The invading fluid was water and the defending fluid was air.…”