Optimizing separate phase light hydrocarbon recovery from contaminated unconfined aquifers

• Published in: Advances in water resources 1998-04, Vol.21 (5), p.339-350
• Main Authors: Cooper, Grant S., Peralta, Richard C., Kaluarachchi, Jagath J.
• Format: Article
• Language: English
• Subjects: aquifers; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; equations; Exact sciences and technology; free-product; groundwater; groundwater contamination; groundwater extraction; hydrocarbons; light non-aqueous phase liquids; multiphase; Natural hazards: prediction, damages, etc; optimization; petroleum; Pollution, environment geology; recovery; regression equations; removal; simulation models; simulation regression optimization model; water purification; wells
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/S0309-1708(97)00005-5

A modeling approach is presented that optimizes separate phase recovery of light non-aqueous phase liquids (LNAPL) for a single dual-extraction 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 detailed 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 minimize residual oil volume and maximize free oil recovery while causing free oil volume to decrease a specified amount. This S/R/O modeling approach implicitly immobilizes the free product plume by reversing the water table gradient while achieving containment. Application to a simple representative problem illustrates the S/R/O model utility for problem analysis and remediation design. When compared with the best steady 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 decisions for hydrogeologists, engineers, and regulators.