Importance of Phase Behavior on the Removal of Residual DNAPLs from Porous Media by Alcohol Flooding

A promising method of accelerating the removal of residual DNAPLs from aquifers involves the mobilization of trapped globules by alcohol flooding. This technology was originally developed in the petroleum industry for the recovery of residual oil after waterflooding. Alcohols can significantly reduce the interfacial tension between the residual DNAPLs and the aqueous phase, allowing for mobilization of trapped globules through pore constrictions. In addition, laboratory batch and column results show that certain alcohols preferentially partition into the DNAPL phase, swelling the residual DNAPL globules considerably and at the same time reducing their density significantly. The swollen DNAPL globules become a relatively continuous phase during flooding, making them much easier to displace than disconnected residuals. Density reduction makes the mobilized DNAPL easier to control, and reduces the potential for further downward migration into uncontaminated portions of the aquifer. Laboratory column results confirm that residual trichloroethylene and tetrachloroethylene globules can be effectively removed from glass bead packings at low upflow gradients using preferentially DNAPL-soluble alcohols.