USING PHASE-DIAGRAMS TO PREDICT THE PERFORMANCE OF COSOLVENT FLOODS FOR NAPL REMEDIATION

Cosolvent flooding using water miscible solvents such as alcohols has been proposed as an in situ NAPL remediation technique. This process i s conceptually similar to enhanced oil recovery (EOR) using alcohols a nd some surfactant formulations. As a result of interest in the EOR as pects of these systems, analytical and graphical methods based on frac tional now theory were developed in the petroleum engineering literatu re for modeling these floods. The existing fractional now solutions ha ve not been used previously in environmental applications of cosolvent flooding, but they are applicable and provide many useful insights in to the process. These applications are discussed, with an emphasis on explaining the mechanisms which tend to mobilize trapped NAPL during a cosolvent flood. The theory provides a simple way to predict the gene ral behavior of a cosolvent flood using the phase diagram. It is concl uded that the one-dimensional performance of a cosolvent flood can be predicted largely by inspection of the ternary phase diagram. In parti cular, the nature of the cosolvent flood depends primarily on the posi tion of the cosolvent injection concentration relative to a critical t ie line extension which passes through the plait point, tangent to the binodal curve.