OPTIMIZING SEPARATE PHASE LIGHT-HYDROCARBON RECOVERY FROM CONTAMINATED UNCONFINED AQUIFERS

A modeling approach is presented that optimizes separate phase recover y of light non-aqueous phase liquids (LNAPL) for a single dual-extract ion well in a homogeneous, isotropic unconfined aquifer. A simulation/ regression/optimization (S/R/O) model is developed to predict, analyze , and optimize the oil recovery process. The approach combines detaile d simulation, nonlinear regression, and optimization. The S/R/O model utilizes nonlinear regression equations describing system response to time-varying water pumping and oil skimming. Regression equations are developed for residual oil volume and free oil volume. The S/R/O model determines optimized time-varying (stepwise) pumping rates which mini mize residual oil volume and maximize free oil recovery while causing free oil volume to decrease a specified amount. This S/R/O modeling ap proach implicitly immobilizes the free product plume by reversing the water table gradient while achieving containment. Application to a sim ple representative problem illustrates the S/R/O model utility for pro blem analysis and remediation design. When compared with the best stea dy pumping strategies, the optimal stepwise pumping strategy improves free oil recovery by 11.5% and reduces the amount of residual oil left in the system due to pumping by 15%. The S/R/O model approach offers promise for enhancing the design of free phase LNAPL recovery systems and to help in making cost-effective operation and management decision s for hydrogeologists, engineers, and regulators. (C) 1998 Elsevier Sc ience Limited. All rights reserved.