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

Surfactant-enhanced aquifer remediation is an emerging technology for aquifers 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 residual 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 surfactant formulations. At relatively low capillary numbers (Nca \u3c 10-3) the surfactant mobilization floods resulted in higher NAPL saturations than for similar Nca pure water floods. These differences in macroscopic saturations are explained by differences in microscale mobilization processes. Solubilization of the residual NAPL remaining after the mobilization stage was dominated by the formation of microscale dissolution fingers, which produced nonequilibrium macroscale NAPL solubilization. A macroemulsion phase also was observed to form spontaneously and persist during the solubilization stage of the experiments