THREE-PHASE FLOW ANALYSIS OF OIL SPILLS IN PARTIALLY WATER-SATURATED SOILS (GROUNDWATER, CONTAMINATION, IMMISCIBLE FLUIDS, PETROLEUM, INFILTRATION)

The frequent occurrence of oil spills and their detrimental effect on groundwater quality require, as a first step for effective control and/or clean-up, that the properties governing the movement of oil in the partially water-saturated zone of the subsoil be well understood. Although the analysis of three-phase flow is not new in petroleum engineering, little has been done to describe the capillary and gravitational flow of oil in partially water-saturated soils.; A three-phase flow model, based on the two-phase flow model of Brooks and Corey, that expresses the dependence of saturation and relative permeability on capillary pressure is presented. Nonlinear saturation and relative permeability functions are incorporated into a Galerkin finite element model that is used to simulate the vertical infiltration of oil in partially water-saturated, porous media.; The adequacy of the numerical model OILSPL is verified by comparing its results with the results obtained from a physical model and with an analytical static equilibrium solution. Numerical instability and oscillation increase proportionally with lambda, and must be controlled by careful calibration of the model and by incorporating techniques such as under-relaxation, or reduction of the time steps, to pseudo-linearize the system.; The results of the sensitivity analysis indicate that the pore size distribution index lambda, does not affect appreciably the infiltration rate, but does affect the sharpness of the infiltrating front. The results also indicate that air pressure build-up develops if no horizontal air flux is permitted.; The net effect of ponding oil in an aquifer, in which no lateral water flow is considered, is to displace water from the vicinity of the capillary fringe, where the ponding occurs, and move it upward. At the same time the elevation of zero water pressure (water table) is raised. The numerically calculated saturation and pressure distribution show a clear convergence toward the analytical steady state solution.; Although some more work may be required to refine the model, particularly with respect to the effect of oil contamination on the gas-water displacement pressure, it is expected that this model will be useful in analyzing oil spill situations and in determining the most effective measures for control and clean-up.