IN SITU MEASUREMENT OF THE FRACTAL DIMENSION OF COLLOID DEPOSITS IN POROUS MEDIA

Clogging, defined as the reduction of permeability, is a major challenge in subsurface remediation, aquifer management, and reservoir hydraulics. Clogging in environmental porous media such as these results from several mechanisms, including deposition of colloids, precipitation of deposits, and growth of biofilms. Previous work indicates that clogging by colloid deposition depends not only on the quantity of colloids, but also on their structure. This presentation reports proof-of-principle results demonstrating that it is possible to use static light scattering (SLS) in index-matched porous media to measure deposit structure in situ, by characterizing the dendritic structure of colloid deposits as a fractal dimension. Specifically, the deposition of polystyrene microspheres is characterized within granular Nafion, where the index-matching fluid is an isopropanol/water mixture. The feasibility of the proposed technique is demonstrated by comparison of the SLS data acquired from stable and unstable colloids in ordinary suspensions to SLS data acquired within index-matched porous medium. These results establish a foundation for future efforts to investigate a possible quantitative link between physical, chemical, and biological conditions, deposit structure, clogging, and consequent effects on flow and transport in porous media.