DNAPL accumulation in wells and DNAPL recovery from wells : model development and application to a laboratory study

International audienceDense nonaqueous phase liquid (DNAPL) accumulation and recovery from wells cannot be accurately modeled through typical pressure or flux boundary conditions due to gravity segregation of water and DNAPL in the wellbore, the effects of wellbore storage, and variations of wellbore inflow and outflow rates with depth, particularly in heterogeneous formations. A discrete wellbore formulation is presented for numerical modeling of DNAPL accumulation in observation wells and DNAPL removal from recovery wells. The formulation includes fluid segregation, changing water and DNAPL levels in the well and the corresponding changes in fluid storage in the wellbore. The method was added to a three-dimensional finite difference model (CompSim) for three phase (water, gas, DNAPL) flow. The model predictions are compared to three-dimensional pilot scale experiments of DNAPL (benzyl alcohol) infiltration, redistribution, recovery, and water flushing. Model predictions match experimental results well, indicating the appropriateness of the model formulation. Characterization of mixing in the extraction well is important for predicting removal of highly soluble organic compounds like benzyl alcohol. A sensitivity analysis shows that the incorporation of hysteresis is critical for accurate prediction. Among the multiphase flow and transport parameters required for modeling, results are most sensitive to soil intrinsic permeability