A geomodel is built for multiple reasons. As such, the output provided back to the team can be very varied.

The geomodel is a 3D visualization tool that helps the whole team discussing about how the different hypotheses made by the team are being translated in 3D. Seeing the model in 3D sometimes leads to a revision of the interpretation, which leads to a revision of the model. The loop continues until the interpretation of the reservoir is validated by the team and the model properly captures what the team had in mind about the reservoir.

If the model is meant to feed a dynamic modeling study, the output will often be a 3D simulation grid. While the internal geometry of a 3D grid made for reservoir modeling reflects the depositional space (Figure 1, see also section 1.5), the internal geometry of the 3D simulation grid is made to optimize fluid flow computations. Simulation grids (Figure 2) have often a “sugar box” mesh. The facies and petrophysical properties, populated in the 3D geological grid (Figure 2A), are transferred into the cells of the 3D simulation grid (Figure 2B) mostly with upscaling techniques.

Engineers sometimes ask why reservoir modelers don’t model directly the properties into the 3D simulation grid. Why do we need a specific grid for reservoir modeling? Comparing Figure 1A and Figure 2B illustrates why: there is no easy way of getting a dipping channel body if a sugar grid geometry is used. Similarly, geologists sometimes ask why engineers can’t use the 3D geological grid for the flow simulation. Such complex grids would slow down the flow simulation and would create numerical instabilities. Engineers need a grid optimized for their needs too.

More details about the different outputs needed by engineers will be given in the three chapters on engineering (reservoir engineering in chapter 6, reserves in chapter 7 and production engineering in chapter 8).