RETINA Simulation™ has the BiCG-Stab standard iterative linear solver which is powered by several pre-conditioners including:
The solver and all the pre-conditioners have been developed and tested by ESTD and are fully customized for reservoir simulation needs. Among them, the CPR method is the cutting-edge pre-conditioner in numerical sciences which is based on the AMG technique. Using the AMG technique along with the CPR method to solve the pressure equation is at the heart of RETINA Simulation™ powerful numerical solver. Especially considering the fact that using the CPR method without the AMG technique will present no industrial benefit. The linear solver of well-known commercial simulators that utilize the Nested-Factorization method as the pre-conditioner are almost the fastest solvers in the market which are mainly suited for models with a dominant directional behavior (mostly z direction) and make use of the nearly structured shape of corner point grids. Therefore using Nested Factorization for simulation of models with high heterogeneity and/or large number of non-neighbor connections (either of which usually occur in giant fractured reservoirs) can result in severe convergency problems. The AMG technology is one of the most recent strategies for solving matrices generated in elliptic partial differential equations that can produce suitable solutions for complicated problems. RETINA Simulation™ has its own customized AMG based solver which is fully tested on more than 50 sets of data from real-world fields, some SPE samples, and many synthetic models. This solver has the power of solving very complex, large and heterogonous models without linear convergency problems. This fact gives RETINA Simulation™ the power to solve models that are simply not solvable using known commercial simulators.