High Resolution X-Ray Differential Phase Contrast for Fluid Imaging in Porous Media*

X-Ray computed tomography is a common technique for determining the three-dimensional structure of solids but has found limited application for measuring the structure of liquid-liquid interfaces within porous media because the X-Ray absorption coefficients tend to be similar for most fluids. Two primary techniques, a high brightness source or added contrast agent, have previously been utilized to enable X-Ray imaging of 3D liquid-liquid interfaces. The use of a high brightness source is expensive and logistically complicated. Adding a contrast agent effects the fluid dynamics that are being observed.
We’ve developed a tool for the high resolution inspection of these 3D liquid-liquid interfaces within porous media by using differential phase contrast (DPC) X-ray imaging. This tool uses a micro-focus x-ray source, paired with a high resolution indirect x-ray detector, along with gold amplitude and phase gratings to measure the index of refraction of the fluids under interrogation along with the absorption coefficient that is normally measured in x-ray microscopy. Using this technique, we show experimental images of oil-water interfaces within porous media.