Pore-Scale Characterization of Organic Immiscible Liquid in Natural Porous Media Using Synchrotron X-ray Microtomography

Abstract

The objective of this study was to characterize the pore-scale morphology of organic immiscible liquid residing within natural porous media. Synchrotron X-ray microtomography was used to obtain high-resolution, three-dimensional images of solid and liquid phases in packed columns. The image data were processed to generate quantitative measurements of organic-liquid blob morphology and organic liquid-water interfacial area. Five porous media comprising a range of median grain-sizes and grain-size distributions were used to evaluate the impact of porous-medium texture on organic-liquid blob morphology. The sizes and shapes of the organic-liquid blobs varied greatly, ranging from small spherical singlets to large, amorphous ganglia. The majority of the total organic-liquid surface area and volume was associated with the largest blobs. The distribution of blob sizes was greatest for the porous medium with the broadest particle-size and pore-size distributions. Organic-liquid blob morphology was additionally compared in two-phase (organic liquid-water) and three-phase (organic liquid-air-water) systems. In the three-phase systems, lenses and films of organic-liquid were observed in contact with air. Lenses were not observed in the two-phase systems. The presence of organic-liquid lenses and films resulted in larger surface area-to-volume ratios. The impact of dissolution on organic-liquid configuration and interfacial areas in two-phase systems was assessed. Organic-liquid blobs decreased in size and number as the columns were flushed. Separation of large multi-pore ganglia into distinct units was observed. Decrease in interfacial area correlated well with the decrease in organic-liquid volume. A one-dimensional first-order mass transfer expression was able to match effluent concentrations reasonably well with a single value of the mass transfer coefficient. In the final component of the study, immiscible-fluid configuration and interfacial areas were compared among organic liquid-water, air-water and air-organic liquid systems for two porous media. For both porous media, the nonwetting-phase configuration and interfacial areas were similar for the three two-fluid pair systems. This indicates that nonwetting phase configuration and wetting-nonwetting phase interfacial area are similar irrespective of the specific fluid pair. Properties of the porous medium appear to have a greater influence on the magnitude of specific total interfacial area for a given saturation than fluid properties or wetting-phase history.