Four-Dimensional Dynamic Synchrotron Microcomputed Tomography Imaging of Gas-Water Interface at High Pressure and Low Temperature

It is challenging to separate water from gas phases in computed tomography images of three-phase granular materials because water and most gases have close attenuation coefficients for x-ray. This article presents two techniques for three-dimensional (3D) imaging using synchrotron microcomputed tomography (SMT). Monochromatic x-ray beam that can be tuned for a specific energy level was used for a dual energy SMT that takes advantage of a sudden change in attenuation at the absorption edge of iodine. A solution of 4 % by weight potassium iodide (KI) and distilled water was used as a doping agent to saturate a column of sand as a test sample. The article focuses on how the technique was employed to image a column of sand as the degree of saturation changes. Water and air were separated easily, and the degree of saturation was calculated for the sand column at different drainage conditions. The article also presents a description of a high-pressure, low-temperature flow cell suitable for SMT imaging for dynamic monitoring of gas hydrate formation and dissociation. High photon flux beam (pink beam) enabled fast 4D imaging (3D plus time) of xenon gas hydrate formation. Hydrate specific area increased initially with increasing hydrate saturation and began to decrease after a threshold, which is evidence of Ostwald Ripening. For hydrate saturation less than 10 %, the predominant pore-habit was surface coating. Cementing pore-habit was observed at 15 % hydrate saturation, and pore-filling hydrate pore-habit was observed with further increase in hydrate saturation.