Role of numerical dispersion in aquifer gas storage modelling

The accuracy of numerical simulation of displacement processes in aquifer systems used as gas storage, and the computing time for these processes are strongly dependent on the selection of grid size and form. For `full-field' models the lateral discretization of the reservoir model should, from a practical point of view, be at least 100 m. However, through the upscaling procedure of fine grid models from meter scale up to coarse grid models in 100 m scale numerical errors are generated, which may compensate or exceed the benefits of enhanced accuracy of upscaled models. Therefore the relationship between numerical errors, which may be attributed to grid coarsening, and the selected grid shape and size are of special importance for the numerical reservoir simulation of aquifer gas storages. Here the properties of displacing gas and displaced water phase emphasize the existence of two main flow regimes - gas overriding and commingled displacement of water by gas. In this study rules are given for the selection of grid size in aquifer storage simulation for the two opposite flow regimes.