Effect of temperature on cosolvent flooding for the enhanced solubilization and mobilization of NAPLs in porous media

This paper examines the potential for enhanced NAPL recovery from the subsurface through the combined application of hot water and cosolvent flushing. Batch experiments were conducted to determine the effect of temperature on fluid properties and the multiphase behavior of the ethanol-water-toluene system and to assess the impact of temperature on the capillary, Bond and total trapping numbers and on flooding stability. Column flooding experiments were also conducted to evaluate toluene NAPL recovery efficiency for different ethanol contents and flushing solution temperatures. The ethanol content considered ranged from 20 to 100% by mass, while the flushing solution temperatures were varied from 10 to 40 °C. It is shown that small variations in the system temperature can strongly influence the solubilization, mobilization and stability of the multiphase system, but that the impact of temperature on the enhanced NAPL recovery is also dependent on the ethanol content of the flushing solution. The impact of hot water on NAPL recovery was most pronounced at intermediate ethanol contents (40-60% by mass) where the increase in system temperature led to enhanced NAPL solubilization as well as NAPL mobilization. This study demonstrates that coupling of hot water with in situ cosolvent flooding is a potentially effective remedial alternative that can optimize NAPL recovery while reducing the amount of chemicals injected into the subsurface.