A GENERALIZED GROWTH-MODEL FOR SIMULATING INITIAL MIGRATION OF DENSE NONAQUEOUS PHASE LIQUIDS

Modeling the migration of spilled non-aqueous phase liquids (NAPLs) is currently difficult because the physics governing their movement is c omplex and knowledge of the local geology is always incomplete. NAPL m ovement is subject to buoyancy, capillary, and viscous forces in addit ion to being directed by the particular structural and hydraulic prope rties of the porous medium. Consideration of buoyancy forces suggests that the flow regime diagram of Lenormand et al. [1988] can be expande d to a third dimension. We develop a generalized growth model, based o n invasion percolation, that captures the essential physics of initial NAPL migration but is simple enough computationally that simulations can be conducted much faster than by using continuum simulation models that attempt to capture all details of the physics. In comparison wit h available experimental data, our model realistically simulates movem ent of a NAPL for a wide range of values of Bond and capillary numbers , in any kind of porous medium. Because this approach allows much fast er and simpler simulation than other approaches, a higher spatial reso lution and/or the use of Monte Carlo methods to reduce the effect of g eological uncertainty becomes a realistic possibility.