HR: 1340h
AN: H33F-0538    [Abstracts]
TI: Simulating Contaminant Transport In Heterogeneous Media Using The Dual Porosity Method
AU: * Zyvoloski, G
EM: gaz@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division, MS T003, Los Alamos, NM 87545 United States
AU: Keating, E
EM: ekeating@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division, MS T003, Los Alamos, NM 87545 United States
AU: Robinson, B
EM: robinson@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division, MS T003, Los Alamos, NM 87545 United States
AU: Lu, Z
EM: zhiming@lanl.gov
AF: Los Alamos National Laboratory, Earth and Environmental Sciences Division, MS T003, Los Alamos, NM 87545 United States
AB: The dual porosity (DP) formulation is a method originally developed for combined fracture and matrix flow. The typical approach would be to solve the normal system of mass and transport equations on a fully-connected grid representing the fracture domain, with one additional equation at each node which corresponds to the matrix domain. In this formulation, the matrix is not a continuous medium, but provides important fluid and energy storage terms to the fracture node equations. A significant limitation of this approach is that there is no ability to capture gradients within the matrix; the original dual porosity method was sometimes called "quasi-steady" because of this limitation. Since the early development of DP methods, advances have been made in solution techniques and also in increasing the number of matrix modes corresponding to each fracture node. We introduce herein a Generalized Dual Porosity Method (GDPM) in which the number of matrix nodes (per fracture node) can vary spatially within a numerical grid. This allows not only the ability to represent gradients and mass -transfer limited processes within the matrix, but also to place additional matrix nodes efficiently. An algebraic decomposition method is presented in which the added complexity of the additional matrix nodes is efficiently solved. We apply a modification of the method to the problem of incorporating sub-grid scale heterogeneity in a sand and clay aquifer into large-scale flow and transport simulations. Here the sand and clay represent the continuous and discontinuous media, respectively. We assume that the mass of contaminant is primarily contained within the clay layers, which is transported via mass-transfer limited mechanisms to the sand medium. We compare several different numerical formulations of this problem: a very fine grid continuum model (truth), and coarse-grid GDPM solution, and intermediate scale continuum model. The models are compared on the basis of accuracy and computational efficiency.
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting