Optimized prefabricated vertical wells for light nonaqueous phase liquid recovery

Work presented herein examines optimization of prefabricated vertical well (PVW) performance during the extraction of light nonaqueous phase liquids (LNAPLs) in liquid and vapor phases in terms of lowering liquid level for promotion of vapor phase extraction, the magnitude of the vacuum head, and the spatial spacing of the PVWs. MATLAB’s genetic algorithm toolbox is linked to BIOSLURP (a multiphase transport finite element program) to achieve specific objectives with respect to time, vacuum level, or PVW spatial location. The optimization process is set up to control the decision variables (input to the BIOSLURP), on the basis of the objective function, defined as: (i) optimum time for lowering water level in view of impact of the residual saturation on free phase extraction processes; (ii) the magnitude of vacuum level for maximum vapor phase mass extraction and time at which air circulation should be adopted based on liquid level within the subsurface; and (iii) the efficient spatial placement of PVWs to maximize the free LNAPL extraction. Results indicated that a higher water saturation (wetting fluid) leads to lower LNAPL (nonwetting fluid) relative permeability and therefore prolonged time to lower the liquid level. Within the range of vacuum levels achieved in the field, there is an optimized vacuum level, which leads to highest extraction rate in the gas phase. Analysis included the feasibility of optimizing PVWs spacing and the illustrated process serves as a guidance approach to specify operating parameters.