This integration would benefit the whole reservoir management process, facilitating the whole team of geophysicists, geoscientists, geologists and engineers to develop a consistent model of the reservoir. To get to this point data flow and management processes need to be carefully developed. Additionally many oil companies have their own in-house simulators. Almost all simulators are finite difference based. The grid structures have been developed to be curvilinear and also they allow Local Grid Refinement where small grids that may have differing grid spacing and coordinate systems are embedded into larger ones.
Most simulators employ a mixture of explicit and implicit formulation.
The modeller needs to balance the stability of an implicit formulation with the greater computation required. By making some assumptions the pressure equations can be solved implicitly, independent of the saturations, and then the saturations calculated. Fully implicit methods may involve the simultaneous calculation of both pressure and saturations or sequential implicit calculations where the variables are still separated out but implicit formulations are used for all variables. These attempt to minimise computation while retaining stability. The saturation equations are then solved along the streamlines described by the velocity field.