Dual - Porosity Reservoir Model with an Improved Coupling Term

A new dual-porosity model is developed for singlephase flow in fractured/porous media. As in the commonly-used approach, flow is assumed to take place through the fracture network, and between the fractures and matrix blocks. The matrix blocks are treated in a lumped-parameter manner, with a single average pressure used for each matrix block. However, instead of assuming that fracture/matrix flux is proportional to the difference between the fracture pressure and matrix pressure at each point, as in the Warren-Root model, a nonlinear equation is used which accurately models the flux at both early and late times. This flux equation is verified against analytical solutions for spherical blocks with prescribed pressure variations on their boundaries. This equation is then used as a source/sink term in the numerical simulator TOUGH. The modified code allows more accurate simulations than the conventional Warren-Root method, and with a large savings in computational time compared to methods which explicitly discretize the matrix blocks.