Enhanced contact of cosolvent and DNAPL in porous media by concurrent injection of cosolvent and air.
Dense nonaqueous phase liquid (DNAPL) contamination is a major environmental problem. Cosolvent flooding is proposed as a remedial alternative to water flooding. The efficacy of cosolvent flooding is a function of the degree of contact between the injected remedial fluid and the resident DNAPL Poor contact may result from remedial fluids traveling in preferential flow paths which bypass trapped DNAPL Thus, the motivation for this study was to use the preferential flow of air in porous media to enhance contact between the injected cosolvent and resident DNAPL The study evaluated concurrent injection of cosolvent and air to improve the spatial extent of DNAPL removal in porous media. A 70% ethanol/30% water (v/v) cosolvent was injected simultaneously with air into a micromodel containing residual tetrachloroethylene (PCE). Double drainage displacement was observed as a dominant DNAPL removal mechanism in the initial period of the cosolvent-air flooding (i.e., gas displaced PCE that displaced water). The residual PCE residing in the preferential paths traversed by air was readily displaced. In addition to this initial PCE mobilization, air flowing through the preferential flow paths displaced cosolvent from these paths into other flow paths and facilitated dissolution of PCE.