The impact of transitions between two-fluid and three-fluidphases on fluid configuration and fluid-fluid interfacial areain porous media.

Multiphase-fluid distribution and flow is inherent in numerous areas of hydrology. Yet, pore-scale characterization of transitions between two and three immiscible-fluids is limited. The objective of this study was to examine the impact of such transitions on the pore-scale configuration of organic liquid in a multi-fluid system comprising natural porous media. Three-dimensional images of an organic liquid (trichloroethene) in two-phase (organic-liquid/water) and three-phase (air/organic-liquid/water) systems were obtained using X-ray microtomography before and after drainage and imbibition. Upon transition from a two-phase to a three-phase system, a significant portion of the organic liquid (intermediate wetting fluid) was observed to exist as lenses and films in contact with air (nonwetting fluid). In these cases, the air was either encased by or contiguous to the organic liquid. The presence of air resulted in an increase in the surface-area-to-volume ratios for the organic-liquid blobs. Upon imbibition, the air was displaced downgradient, and concomitantly, the morphology of the organic-liquid blobs no longer in contact with air reverted to that characteristic of a two-phase distribution (i.e., more spherical blobs and ganglia). This change in morphology resulted in a reduction in the surface-area-to-volume ratio. These results illustrate the impact of transitions between two-phase and three-phase conditions on fluid configuration, and they demonstrate the malleable nature of fluid configuration under dynamic, multiphase-flow conditions. The results have implications for characterizing and modeling pore-scale flow and mass-transfer processes.

In situ oxidation and associated mass-flux-reduction/mass-removal behavior for systems with organic liquid located in lower-permeability sediments.

The effectiveness of permanganate for in situ chemical oxidation of organic liquid (trichloroethene) trapped in lower-permeability (K) zones located within a higher-permeability matrix was examined in a series of flow-cell experiments. The permanganate solution was applied in both continuous and pulsed-injection modes. Manganese-oxide precipitation, as confirmed by use of SEM-EDS, occurred within, adjacent to, and downgradient of the lower-K zones, reflective of trichloroethene oxidation. During flow interruptions, precipitate formed within the surrounding higher-permeability matrix, indicating diffusive flux of aqueous-phase trichloroethene from the lower-K zones. The impact of permanganate treatment on mass flux behavior was examined by conducting water floods after permanganate injection. The results were compared to those of water-flood control experiments. The amount of water flushing required for complete contaminant mass removal was reduced for all permanganate treatments for which complete removal was characterized. However, the nature of the mass-flux-reduction/mass-removal relationship observed during water flooding varied as a function of the specific permanganate treatment.