Three-dimensional flow in heterogeneous geologic media

Overview & Synopsis

An efficient numerical code is used for modeling detailed subsurface flow systems in unsaturated, partially saturated, or saturated porous formations with fully three-dimensional heterogeneous material properties . This paper describes numerical strategy, computational requirements, and numerical tests, and presents large simulation results for saturated and unsaturated flow in highly heterogeneous,three-dimensionalgeologic formations. The main computational requirements arise from constraints on space-time discretization in the presence of heterogeneity and nonlinearity. Numerical errors due to discretization and iterative solution can be assessed by numerical analysis, and through internal tests such as conservation of mass and comparisons between fine and coarse mesh solutions. Two large model problems, with three-dimensional grids on the order of several hundred thousand nodes, are presented. The first problem, implemented on a minicomputer, deals with steady-state groundwater flow in an imperfectly stratified, heterogeneous aquifer with statistically anisotropic , spatially random hydraulic conductivity. The second model problem, implemented on a supercomputer, concerns the case of transient strip-source infiltration and drainage in an imperfectly stratified soil with a statistically anisotropic, spatially random unsaturated conductivity-pressure curve