A NEW LUMPED-PARAMETER MODEL FOR FLOW IN UNSATURATED DUAL-POROSITY MEDIA

A new lumped-parameter approach to simulating unsaturated flow process es in dual-porosity media such as fractured rocks or aggregated soils is presented. Fluid flow between the fracture network and the matrix b locks is described by a non-linear equation that relates the imbibitio n rate to the local difference in liquid-phase pressure between the fr actures and the matrix blocks. Unlike a Warren-Root-type equation, thi s equation is accurate in both the early and late time regimes. The fr acture/matrix interflow equation has been incorporated into an existin g unsaturated flow simulator, to serve as a source/sink term for fract ure gridblocks. Flow processes are then simulated using only fracture gridblocks in the computational grid. This new lumped-parameter approa ch has been tested on two problems involving transient flow in fractur ed/porous media, and compared with simulations performed using explici t discretisation of the matrix blocks. The new procedure seems to accu rately simulate flow processes in unsaturated fractured rocks, and typ ically requires an order of magnitude less computational time than do simulations using fully-discretised matrix blocks. Copyright (C) 1996 Elsevier Science Limited