HR: 17:30h
AN: H44D-07    [Abstracts]
TI: Pore-Network Model Investigation of Stability & Scaling of Immiscible Displacement Fronts with Buoyancy Forces
AU: * Benito, P H
EM: pbenito@berkeley.edu
AF: U.C. Berkeley, Dept. Civil & Environmental Engineering, 431 Davis Hall, U.C. Berkeley, Berkeley, CA 94720, United States
AU: Patzek, T
EM: patzek@ce.berkeley.edu
AF: U.C. Berkeley, Dept. Civil & Environmental Engineering, 431 Davis Hall, U.C. Berkeley, Berkeley, CA 94720, United States
AB: Understanding the behavior and geometry of multi-phase immiscible displacement fronts is critical in the fields of environmental restoration, geologic hazardous waste storage, and petroleum engineering ( e.g. air sparging, NAPL infiltration, and secondary recovery of petroleum by water flooding). Depending on the flow conditions, the presence of gradients, such as those caused by gravity forces, viscous forces or permeability gradients, can variously lead to either stabilized ( e.g. piston-like) or to unstable ( e.g. gravity or viscous fingering) displacement fronts. Previous studies have found that the resulting displacement fronts may have patterns with percolation, or fractal, characteristics which cannot be adequately described by continuum equations [Chaouche et al., 1994; Glass & Yarrington, 1996; and, Zhang et al., 2000]. Numerical pore-network models which incorporate the appropriate physics provide a framework in which to study these characteristics of flow in porous materials. We present results of numerical simulations on regular two-dimensional lattices which are based on the method of invasion percolation in a gradient (IPG). The pore-network is populated with pore throats and bodies whose radii are drawn from a random statistical distribution. The network is initially water saturated and then invaded by a non-wetting fluid (drainage). Both capillary and buoyancy forces are included to define a filling potential for each pore. The invasion advances in quasi-static steps, by increasing the capillary pressure and invading accessible pores with the lowest filling potential at each step. The wetting phase can become trapped in pores that become isolated from the outlet face. Simulations were run over a range of Gravity Bond Number (the ratio of characteristic buoyancy and capillary forces). We identify the regimes in which stable and unstable displacement occurs and we examine how the fractal geometry of the displacement front, the saturation, capillary pressure, and relative permeability of each phase varies with the Bond Number. We also confirm the power-law scaling of the front width and the non-wetting phase saturation with the Bond Number as derived from percolation theory.
DE: 1831 Groundwater quality
DE: 1832 Groundwater transport
DE: 1839 Hydrologic scaling
DE: 1847 Modeling
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting