Wettability is one of the critical parameters affecting multiphase flow in porous media. The wettability is determined by the affinity of fluids to the rock surface, which varies due to factors such as mineral heterogeneity, roughness, ageing, and pore-space geometry. It is well known that wettability varies spatially in natural rocks, and it is still generally considered a constant parameter in pore-scale simulation studies. The accuracy of pore-scale simulation of multiphase flow in porous media is undermined by such inadequate wettability models. The advent of in situ visualization techniques, e.g. X-ray imaging and microtomography, enables us to characterize the spatial distribution of wetting more accurately. There are several approaches for such characterization. Most include the construction of a meshed surface of the interface surfaces in a segmented X-ray image and are known to have significant errors arising from insufficient resolution and surface-smoothing algorithms. This work presents a novel approach for spatial determination of wetting properties using local lattice-Boltzmann simulations. The scheme is computationally efficient as the segmented X-ray image is divided into subdomains before conducting the lattice-Boltzmann simulations, enabling fast simulations. To test the proposed method, it was applied to two synthetic cases with known wettability and three datasets of imaged fluid distributions. The wettability map was obtained for all samples using local lattice-Boltzmann calculations on trapped ganglia and optimization on surface affinity parameters. The results were quantitatively compared with a previously developed geometrical contact angle determination method. The two synthetic cases were used to validate the results of the developed workflow, as well as to compare the wettability results with the geometrical analysis method. It is shown that the developed workflow accurately characterizes the wetting state in the synthetic porous media with an acceptable uncertainty and is better to capture extreme wetting conditions. For the three datasets of imaged fluid distributions, our results show that the obtained contact angle distributions are consistent with the geometrical method. However, the obtained contact angle distributions tend to have a narrower span and are considered more realistic compared to the geometrical method. Finally, our results show the potential of the proposed scheme to efficiently obtain wettability maps of porous media using X-ray images of multiphase fluid distributions. The developed workflow can help for more accurate characterization of the wettability map in the porous media using limited experimental data, and hence more accurate digital rock analysis of multiphase flow in porous media.
A fast pink‐beam X‐ray microtomography methodology was developed at the GSECARS 13‐BMD beamline at the Advanced Photon Source to study multiphase flow in porous media. The white beam X‐ray distribution of the Advanced Photon Source is modified using a 1‐mm copper filter and the beam is reflected off a platinum mirror angled at 1.5 mrad, resulting in a pink beam with X‐ray intensities predominately in the range of 40–60 keV. Bubble formation in the wetting phase and wettability alteration of the solid phase from x‐ray exposure can be a problem with high flux and high energy beams, but the suggested pink‐beam configuration mitigates these effects. With a 14‐second acquisition time for capturing a complete dataset, the evolving fluid‐fronts of nonequilibrium three‐dimensional multiphase flow can be studied in real‐time and the images contain adequate image contrast and quality to measure important multiphase quantities such as contact angles and interfacial areas.
Understanding how fluids are transported through porous materials is pertinent to many important societal processes in the environment (e.g. groundwater flow for drinking water) and industry (e.g. drying of industrial materials such as pulp and paper). To develop accurate models and theories of this fluid transportation, experiments need to track fluids in 3‐dimensions quickly. This is difficult to do as most materials are opaque and therefore cameras cannot capture fluid movement directly. But, with the help of x‐rays, scientists can track fluids in 3D using an imaging technique called x‐ray microtomography (μCT). Standard μCT takes about 15 minutes for one image which can produce blurry images if fluids are flowing quickly through the material. We present a technique, fast μCT, which uses a larger spectrum of x‐rays than the standard technique and acquires a 3D image in 14 seconds. With the large amount of x‐rays utilized in this technique, bubbles can start to form in the fluids from x‐ray exposure. We optimized the utilized x‐ray spectrum to limit bubble formation while still achieving a rapid 3D image acquisition that has adequate image quality and contrast. With this technique, scientists can study fluid transport in 3D porous materials in near real‐time for the improvement of models used to ensure public and environmental health.
- PAR ID:
- 10458233
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Journal of Microscopy
- Volume:
- 277
- Issue:
- 2
- ISSN:
- 0022-2720
- Page Range / eLocation ID:
- p. 100-106
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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