Pore Scale Visualization of Drainage in 3D Porous Media by Confocal Microscopy

Abstract

We visualize the dynamics of immiscible displacement of a high viscosity wetting phase by a low viscosity non-wetting phase in a three-dimensional (3D) glass bead packing using confocal microscopy. Both phases were doped with two different fluorescent dyes, which enabled visualization of both phases simultaneously and quantification of the phase volumes without the need of image subtraction operations. The transient results show details of the displacement process and how pores are invaded by the non-wetting displacing phase. The static images at the end of the displacement process reveal how the trapped ganglia volume and morphology change with capillary number. The wetting phase is trapped as pendular rings spanning one to multiple pore necks. Details of the pore scale flow of oil wet media revealed with the experimental methods presented here can lead to better fundamental understanding of the physical processes and optimized enhanced oil recovery methods, CO₂ sequestration and aquifer remediation.

Figure 1

3D rendering images showing the dynamic behavior of drainage. (a) Showing both the displaced wetting (yellow) and displacing non-wetting (blue) phases and (b) showing only the non-wetting liquid.

Figure 2

Evolution of the non-wetting invading phase saturation showing Haines jump.

Figure 3

Rendering of  3D images acquired at steady state after the injection of the displacing fluid at different capillary numbers, which contemplates both phases: wetting (yellow) and non-wetting (blue) fluids.

Figure 4

Saturation of the displaced phase as a function of the capillary number.

Figure 5

Volume of trapped displaced phase ganglia as a function of capillary number.

Figure 6

Geometric parameters of the largest trapped displaced phase ganglia as a function of capillary number (a) volume and (b) length along the flow direction.

Figure 7

Trapped ganglia size distribution as a function of capillary number.

Figure 8

Sphericity of trapped ganglia as a function of their volume for different capillary numbers.

Figure 9

3D images showing both the displacing non-wetting (blue) and displaced wetting (yellow) phases in four different positions along the porous media to exemplify different ganglia morphology. The trapped ganglia are in the form of pendular rings, spanning one, three and multiple pore necks.

Figure 10

3D processed images with ganglia volume colored according to the scale bar.

Figure 11

Schematic illustrations of (a) image acquisition and 3D rendering process; (b) the wetting fluid (yellow) been displaced by the non-wetting fluid (blue); and (c) residual fluids after the drainage process.

Figure 12

Image processing sequence for two representative slices. Top 4: Slice 1, at the bottom wall. Bottom 4: Slice 80, 192 µm depth. (a,e) Original images. (b,f) After histogram equalization. (c,g) After noise reduction with Sigma filter. (d,h) After segmentation with the Otsu method.