Displacement of nonaqueous phase organic liquids from saturated sands with surfactant foams.

Abstract

In this research, a decontamination technique using foam generated from mixing a surfactant solution and air was investigated. A systematic approach was employed to investigate the process for its effectiveness and efficiency in comparison to flushing with solutions of the surfactants, for its effectiveness in different experimental dimensions, for its macroscopic behavior, and for its microscopic mechanisms by which it displaces organic globules. This research showed that surfactant foam flushing had an efficiency more than 10 times higher than that of either surfactant solution flushing or conventional water flooding, based on the volume of liquid solution used. The Young-Laplace Equation was shown to predict the pressure required in different sands. Due to this capillary resistance, the viscosity of foam was several times higher than either of its constituents. In addition to the pore size of sand, the surfactant, the air flowrate and pressure, the quality, stability, and bubble-size distribution of the foam, and the organic liquid all had an influence on the performance of foam flushing. Based on the results of the microscopic investigation, the efficiency of surfactant foam was attributed to its enhancement of the mobilization mechanism. Foam effectively broke up the residual organic liquid globules into smaller spheres. The smaller globules then moved easily with the ambient liquid. This destructive type of mobilization is more effective than the conventional mobilization. The research is unique in many aspects: it was one of the first studies in environmental remediation to employ surfactant foam to remove organic liquids; it identified the effects of surface tension and pore size on foam behavior; it analyzed the impacts of sand, surfactant, and air on the removal of different organic liquids; and it provided direct visual evidence of mobilization of organic globules by foam bubbles. The information from these results forms a basis for applying the process in the field. According to the information provided in this research, the surfactant to be used for foam flushing should have a lower surface tension to enhance foam generation and advancement, and it should be able to generate foam with enough stability to interact with organic liquids. Based on the values of viscosity or permeability derived in this research, the influence zone of foam flushing can be for a given injection pressure. Internal foam generation, combined with alternating injection of air and solution, should provide a better recovery efficiency for a given organic liquid-surfactant foam system.