EFFECT OF SUBSURFACE HETEROGENEITY ON FREE-PRODUCT RECOVERY FROM UNCONFINED AQUIFERS

Free-product recovery system designs for light-hydrocarbon-contaminate d sites were investigated to evaluate the effects of subsurface hetero geneity using a vertically integrated three-phase flow model. The inpu t stochastic variable of the areal flow analysis was the log-intrinsic permeability and it was generated using the Turning Band method. The results of a series of hypothetical field-scale simulations showed tha t subsurface heterogeneity has a substantial effect on free-product re covery predictions. As the heterogeneity increased, the recoverable oi l volume decreased and the residual trapped oil volume increased. As t he subsurface anisotropy increased, these effects together with free- and total-oil contaminated areas were further enhanced. The use of mul tiple-stage water pumping was found to be insignificant compared to st eady uniform pumping due to reduced recovery efficiency and increased residual oil volume. This observation was opposite to that produced un der homogeneous scenarios. The effect of subsurface heterogeneity was enhanced at relatively low water pumping rates. The difference in resu lts produced by homogeneous and heterogeneous simulations was substant ial, indicating greater attention should be paid in modeling free-prod uct recovery systems with appropriate subsurface heterogeneity.