Analytical solutions for surfactant-enhanced remediation of nonaqueous phase liquids

Benchmark compositional solutions are presented for the remediation of aquifers contaminated with nonaqueous phase liquids (NAPLs) by injection of surfactant-water mixtures. The method of characteristics (MOC) is used to find one-dimensional analytical solutions to the Riemann problem where three partially miscible phases are flowing in a Winsor type III microemulsion. In partially miscible flow, two or three phases form when the components (constituents) are mixed in some but not all proportions. Three relative permeability models are examined, and MOC solutions are found. Fine-grid numerical simulations match the MOC results. The composition routes and contaminant recoveries can differ significantly depending on the relative permeability model used. The results for each model are optimized to determine the minimum surfactant volume required for complete contaminant recovery. Unlike two-phase partially miscible flow, the presence of three flowing phases makes it impossible to reach miscibility between the injected and resident fluids, regardless of surfactant concentration.