Laplace transform Galerkin technique for large-scale simulation of mass transport in discretely fractured porous formations

293A 925156 Upscaling of hydraulic conductivity in partially saturated heterogeneous porous formation Russo, D Water Resoar Res V28, N2o Feb 1992, P397-409 Hydraulic properties of geological media vary irregularly in space, and it is often necessary to upscale values from those at the scale of measurement to those at the scale at which they will be applied. An approach to do this is presented, based on the concept of block conductivity (ratio of volume-averaged flux to volume-averaged head gradien0. Point values of formation properties are viewed as realisations of independent random spatial functions. Means of replacing point properties by block properties of the porous medium, which are functions of the intrinsic properties of the material and of block size, are described. A combination of stochastic theory for steady unsaturated flow and a block-averaging theory for saturated steady flow is used. 925157 Laplace transform Galerkin technique for large-scale simulation of mass transport in discretely fractured porous formations Sudicky, E A; McLaren, R G Water Resour Res V28, N2, Feb 1992, P499-514 Traditional modelling techniques have severe limitations in investigation of contaminant migration in porous media containing a network of discrete fractures. To overcome these difficulties, the application of the Laplace transform Galerkin technique is proposed. This avoids time stepping and allows use of relatively coarse grids without loss of accuracy. The O R T H O M I N accelerated iterative solver is presented for increased computational efficiency. Advective-dispersive porous matrix transport and dual porosity theory to describe matrix transport in microfractured regions can be accommodated. Its application to an example problem indicates that flow in essentially undetectable fractures in aquitard layers may be important to aquifer contamination. 925158 Numerical analysis of solute migration through fractured clayey deposits into underlying aquifers Harrison, B; Sudicky, E A; Cherry, J A Water Resour Res V28, N2, Feb 1992, P515-526 Field studies indicate that clayey aquitards which were previously considered unfractured may contain vertical fractures which actively transmit groundwater and may act as contaminant conduits. Using a 2D Laplace transformation Galerkin finite element model (ibid, V28, N2, P499-514), the importance of idealised vertical plane fractures to flow and transport through a 15m thick aquitard is examined. Sensitivity analysis indicates that presence of fractures of apertures as small as l0 microns (which are extremely difficult to detect or identify) can lead to development of significant contaminant plumes. 925159 Perspective on the numerical solution of convection-dominated transport problems: a price to pay for the easy way out Noorishad, J; Tsang, C F; Perrochet, P; Musy, A Water Resour Res V28, N2, Feb 1992, P551-561 The evolution of numerical techniques used to solve convection-dominated transport problems is reviewed. Successful approaches and their limitations are discussed. The performance characteristic of the Crank-Nicholson Galerkin finite element method is obtained in terms of a curve of Peclet number

against Courant number. A simple upwind criterion is proposed for the CNG FEM, which overcomes the difficulties encountered in the solution of the sharp front transport problem over the whole range of Peeler and Courant numbers, at the expense of some optimal smearing along the streamlines.

925160 Simulation of large-scale transport of variable density and viscosity fluids using a stochastic mean model Welty, C; Geihar, L W Water Resoar Res V28, N3, March 1992, P815-827 Stochastic analysis of the coupled miscible transport problem shows macrodispersivity is a function of the properties of the displacing and displaced fluids as well as porous material properties. The dependence of macrodispersivity on mean concentration and concentration gradient gives rise to a nonlinear mean solute transport equation, which is here examined using a ID finite difference formulation. For solute concentrations of environmental significance, density effects give rise to macrodispersivities several orders of magnitude different from the ideal tracer case. For the case where solute concentrations differ greatly (such as secondary petroleum recovery), viscosity effects have the predominant influence on macrodispersivity.

925161 Effect of heterogeneity on the drainage capillary pressuresaturation relation Ferrand, L A; Celia, M A Water Resour Res V28, N3, March 1992, P859-870 Mathematical description of multiphase fluid displacement in porous media requires knowledge of the relation between capillary pressure and saturation. The relation can be measured at laboratory scale, but upscaling is difficult in heterogeneous media. A method for this scaling, based on percolation theory, is presented. Numerical results based on network models show that heterogeneities have a significant influence on the effective relations, and that procedures based on linear averaging of individual relations can lead to errors.

925162 Numerical method for aquifer parameter estimation utilizing environmental tracers in a transient flow system Adar, E M; Sorek, S Proc Conference on Calibration and Reliability in Groundwater Modelling, The Hague, 3-6 September 1990 P135-148. Publ Wailingford: IAHS Press, 1990 (1AHS Publication No. 195) Many basins have complex geological structures for which limited hydrological information is available. A method is proposed for such situations to assess the spatial distribution of hydraulic parameters on the basis of observed spreading of environmental tracers. The model uses the lumped parameter approach with the aquifer subdivided into a finite number of cells. Transmissivities and inflows are obtained by optimising a set of mass balance equations. Storativities are assessed using a Gauss-Markov optimisation approach to predict changes in piezometric head. Model validation against synthetic data is presented.

© 1992 Pergamon Press Ltd. Reproduction not permitted RMMS 29/~-- H