Accuracy and efficiency of a semi-analytical dual-porosity simulator for flow in unsaturated fractured rock masses

A semi-analytical dual-porosity simulator for unsaturated flow in fractured rock masses has been developed. Fluid flow between the fracture network and the matrix blocks is described by analytical expressions that have been derived from approximate solutions to the imbibition equation. These expressions have been programmed into an unsaturated flow simulator, TOUGH, as a source/sink term. Flow processes are then simulated using only fracture elements in the computational grid. The modified code is used to simulate flow along single fractures, and infiltration into pervasively fractured formations. Comparisons are made with simulations carried out using discretization of both the fractures and matrix blocks. The new semi-analytical code is shown to be accurate, and typically requires an order of magnitude less computational time. (author) figs., tabs., refs