Visualization of surfactant-enhanced nonaqueous phase liquid mobilization and solubilization in a two-dimensional micromodel

Surfactant-enhanced aquifer remediation is an emerging technology for aquif ers contaminated with nonaqueous phase liquids (NAPLs). A two-dimensional! micromodel and image capture system were applied to observe microscale NAPL mobilization and solubilization phenomena. In each experiment a common res idual NAPL field was established, followed by a series of mobilization and solubilization experiments. Mobilization floods included pure water floods with variable flow rates and surfactant; floods with variations in surfacta nt formulations. At relatively low-capillary numbers (N-ca < 10(-3)) the su rfactant mobilization floods resulted In higher NAPL saturations than for s imilar N-ca pure water floods. These differences in macroscopic saturations are explained by differences in microscale mobilization processes. Solubil ization of the residual NAPL remaining after the mobilization stage was dom inated by the formation of microscale dissolution fingers, which produced n onequilibrium macroscale NAPL solubilization. A macroemulsion phase also wa s observed to form spontaneously and persist during the solubilization stag e of the experiments.