Characterizing pore-scale dissolution of organic immiscible liquid in natural porous media using synchrotron X-ray microtomography

The objective of this study was to characterize the pore-scale dissolution of organic immiscible-liquid blobs residing within natural porous media. Synchrotron X-ray micro-tomography was used to obtain high-resolution, three-dimensional images of the aqueous, organic-liquid, and solid phases residing in columns packed with one of two porous media. Images of the packed columns were obtained after a stable, discontinuous distribution (e. g., residual saturation) of the organic liquid (trichloroethene) had been established, and three subsequent times during column flushing. These data were used to characterize the morphology of the organic-liquid blobs as a function of dissolution, and to quantify changes in total organic-liquid volume, surface area, and water-organic liquid interfacial area. The dissolution dynamics of individual blobs appeared to be influenced by the local pore configuration. In addition to dissolution-induced shrinkage, some blobs were observed to separate into multiple distinct subunits. The median blob size decreased by approximately a factor of 2 at the point where approximately 90% of the initial organic-liquid volume had been removed. The ratio of capillary associated interfacial area to total water-organic liquid interfacial area increased by 50% at the point where approximately 95% of the initial mass had been removed. A nearly linear relationship was observed between both total and capillary associated interfacial area and organic liquid volumetric fraction. Changes in the measured aqueous-phase trichloroethene effluent concentrations were well correlated with changes in the volume, surface area, and number of blobs. The effluent concentration data were adequately described by a first-order mass transfer expression employing a constant value of the mass-transfer coefficient, with values for the water-organic liquid interfacial area obtained independently from the microtomography data.