3D hybrid mesh generation for reservoir simulation

A great challenge for flow simulators of new generation is to gain more accuracy at well proximity within complex geological structures. For this purpose, a new approach based on hybrid mesh modelling was proposed in 2D by Balaven et al. (Proceedings of the 7th International Conference on Numerical Grid Generation in Computational Field Simulations, Whistler, Canada, 2000; 407–416). In this hybrid mesh, the reservoir is described by a structured quadrilateral mesh and drainage areas around wells are represented by radial circular meshes. In order to generate a global conforming mesh, unstructured transition meshes constituted by convex polygonal elements satisfying finite volume properties are used to connect these two structured meshes. The hybrid mesh allows us to take full advantage of the simplicity and practical aspects of structured meshes, while complexity inherent to unstructured meshes is introduced only where strictly needed. This paper presents the 3D extension of the generation of such a hybrid mesh (ECCOMAS, Jyväskylä, Finland, 2004). The proposed method uses 3D power diagrams to generate the transition mesh. Due to the round-off errors, this mesh is modified in order to ensure the conformity with the structured meshes. In addition, some criteria are introduced to measure the mesh quality, as well as an optimization procedure to remove or to expand small edges of the transition mesh under finite volume properties constraints. Numerical results are given to show the efficiency of the approach