STEPWISE PUMPING APPROACH TO IMPROVE FREE PHASE LIGHT-HYDROCARBON RECOVERY FROM UNCONFINED AQUIFERS

A stepwise, time-varying pumping approach is developed to improve free phase oil recovery of light non-aqueous phase liquids (LNAPL) from a homogeneous, unconfined aquifer. Stepwise pumping is used to contain t he floating oil plume and obtain efficient free oil recovery. The pump ing approach is developed using detailed simulations, multiple linear regression and graphical plots. The approach uses ARMOS(C), an areal t wo-dimensional multiphase flow, finite-element simulation model. Syste matic simulations of free oil area changes to pumping rates are analyz ed. Pumping rates are determined that achieve LNAPL plume containment at different times (i.e. 90, 180 and 360 days) for a planning period o f 360 days. These pumping rates are used in reverse order as a stepwis e (monotonically increasing) pumping strategy. This stepwise pumping s trategy is analyzed further by performing additional simulations at di fferent pumping rates for the last pumping period. The final stepwise pumping strategy is varied by factors of -25% and +30% to evaluate sen sitivity in the free oil recovery process. Stepwise pumping is compare d to steady pumping rates to determine the best free oil recovery stra tegy. Stepwise pumping is shown to improve oil recovery by increasing recovered oil volume (11%) and decreasing residual oil (15%) when comp ared with traditional steady pumping strategies. The best stepwise pum ping strategy recovers more free oil by reducing the amount of residua l oil left in the system due to pumping drawdown. This stepwise pumpin g approach can be used to enhance free oil recovery and provide for co st-effective design and management of LNAPL cleanup.