Foam injection for enhanced recovery of diesel fuel in soils: Sand column tests monitored by CT scan imagery.

The use of surfactant foam for the remediation of diesel fuel, a Light Non-Aqueous Phase Liquid (LNAPL), was investigated in sand column experiments using X-ray Computed Tomography (CT). A preliminary series of tests were carried out on six surfactant candidates in order to measure their physical properties, including critical micelle concentrations and interfacial tensions (IFT) with the LNAPL. Batch tests for foam stability were carried out with and without added LNAPL, in order to measure the half-life of foam columns produced with each surfactant candidate. Foam flow-rate co-injection tests were carried out for each surfactant candidate in 405 cm sand columns contaminated with LNAPL at residual saturation. These tests revealed that a 1:1 mixture of sodium dodecyl sulfate and cocamidopropyl betaine, injected at a total volumetric flow-rate (Q) of 45 mL/min, resulted in successful generation and propagation of foam within the contaminated porous medium. Finally, two sand column tests, carried out respectively under high- and low-pressure conditions, were imaged with a CT-scanner in order to compare and contrast foam morphology evolution as well as the LNAPL desaturation dynamics involved in both scenarios. The saturation profiles extracted from CT images provided valuable new insights.