Comparison of iterative methods for computing the pressure field in a dynamic network model

In dynamic network models, the pressure map (the pressure in the pores) mus t be evaluated at each time step. This calculation involves the solution of a large number of nonlinear algebraic systems of equations and accounts fo r more than 80 of the total CPU-time. Each nonlinear system requires at lea st the partial solution of a sequence of linear systems. We present a compa rative study of iterative methods for solving these systems, where we apply both standard routines from the public domain package ITPACK 2C and our ow n routines tailored to the network problem. The conjugate gradient method, preconditioned by symmetric successive overrelaxation, was found to be cons istently faster and more robust than the other solvers tested. In particula r, it was found to be much superior to the successive overrelaxation techni que currently used by many researchers.