On the challenges of measuring interfacial characteristics of three‐phase fluid flow with x‐ray microtomography

Abstract

SummarySynchrotron-based x-ray computed microtomography contributes high-resolution, three-dimensional observations to investigations of multiphase fluid transport in porous media. Pore-scale observations are valuable to the development and validation of new theory, as well as numerical models. Computed microtomography has been used previously to measure fluid content and interfacial areas in systems containing two fluids (air-water, oil-water) and to a limited extent to measure fluid content and entrapped fluid morphology in systems containing three fluids (air-oil-water). This study addresses challenges that arise when imaging three-phase flow in spreading systems. The first challenge is related to wettability alteration. Observations reported herein suggest that the wettability of solid surfaces changed over the course of a three-fluid phase flow experiment, a phenomenon that has not been observed in similar, previously conducted two-fluid phase experiments. Follow-up experiments showed that wettability alteration is significant when oil-solid contact is combined with x-ray exposure, and is not reversed with a conventional cleaning procedure. The second challenge arises in segmenting three-phase images, and thereby obtaining data from which various measures can be quantified with sufficient accuracy. Partial volume effects and blur often cause the grey-scale values of different fluids to overlap and appropriate steps must be taken to avoid ambiguity at phase boundaries. A comparison of images collected at standard resolution (10.6 microns voxel -1 ) to those collected at a higher resolution (5.3 microns voxel -1 ) showed that saturation measurements are within 5% of each other, but interfacial areas for three-phase systems may be underestimated at standard resolution by as much as 25%.

3D mapping of water in oolithic limestone at atmospheric and vacuum saturation using X-ray micro-CT differential imaging

“…At first sight, X-ray tomography is not very suitable for directly visualizing water inside a natural rock due to the low contrast of water in comparison with the contrast of the stone. However by using X-ray opaque fluids, it is possible to clearly visualize fluids inside the rock and study multiphase fluid distributions [18,19]. By generating a differential image of a micro-CT image of a rock in a dry state and a micro-CT image of the rock in a state saturated with an X-ray opaque fluid, it is possible to map the distribution of micro-and macropores [12,20].…”

Image processing of multiphase images obtained via X‐ray microtomography: A review

“…Brown et al . [] compared surface area densities of smooth fluid interfaces for the same kind of three‐fluid samples when improving the image resolution from 10.6 to 5.3 μm and observed an increase in the range of 5–16%, depending on the specific fluid pair. An improvement in resolution usually comes at the cost of a smaller field of view as far as industrial scanners are concerned, as well as increased noise unless the scan time is increased as well.…”

“…We refer the reader to Brown et al . [] where we demonstrate that a single‐energy method outperforms a three‐energy method and discuss the potential shortcomings of either approach. All of the surveyed methods are locally adaptive, i.e., in addition to global histogram information they consider some neighborhood statistic for class assignment.…”

In-Situ High Resolution Dynamic X-ray Microtomographic Imaging of Olive Oil Removal in Kitchen Sponges by Squeezing and Rinsing

“…However, the possibilities of imaging olive oil in water simultaneously are limited due to the low difference in X-ray attenuating coefficients at the X-ray energies commonly used in μCT [22]. Low contrast driven by small density differences can be countered by the application of X-ray contrast agents which can bind with specificity to the olive oil constituents and enhance its X-ray attenuation against water and PU (Polyurethane).…”