A NUMERICAL DUAL-POROSITY MODEL WITH SEMIANALYTICAL TREATMENT OF FRACTURE MATRIX FLOW

A new dual-porosity model is developed for single-phase fluid flow in fractured/porous media. Flow is assumed to take place through the frac ture network and between the fractures and matrix blocks. The matrix b locks are treated in a lumped parameter manner, with a single average pressure used for each matrix block. Rather than assuming that fractur e/matrix flux is proportional to the difference between the fracture p ressure and matrix pressure at each point, as is done in the Warren-Ro ot model, we use a nonlinear equation which more accurately models the flux over all time regimes, including both early and late times. This flux equation is compared with analytical solutions for spherical blo cks with prescribed pressure variations on their boundaries. The nonli near flux equation is also used as a source/sink term in the numerical simulator TOUGH. The modified code allows more accurate simulations t han the conventional Warren-Root method, with a large savings (about 9 0%) in computational time compared to methods which explicitly discret ize the matrix blocks.