Hybrid Mesh Generation for Local Grid Refinement in Reservoir Flow Simulation

Mesh generation becomes a crucial step in reservoir flow simulation of new generation. The mesh must faithfully represent the architecture of the reservoir and its heterogeneity. For more accuracy, the mesh must also follow the flow directions in the well vicinity. The current industrial standard meshes based on Corner Point Geometry (CPG) grids have already shown their limits. They are very practical and easy to use, but they fail to represent complex objects due to their structured aspect. More recently, other approaches have been proposed, in particular using the PErpendicular BIssector (PEBI) grids, which are completely unstructured. These grids are very flexible and can model most complex shapes. But, they are often difficult to manage in 3D due to their lack of structure.<br><br>A three dimensional hybrid mesh model was proposed, in ECMOR 9, to capture the radial characteristics of the flows around the wells. In this hybrid mesh, the reservoir is described by a non uniform Cartesian structured mesh and the drainage areas around the wells are represented by structured radial circular meshes. Unstructured polyhedral meshes are used to connect these two kinds of structured grids. The construction of these transition meshes is based on 3D Power Diagrams to ensure finite volume properties : mesh conformity, dual orthogonality and cell convexity. In this paper, we propose an extension of this hybrid model to the case of real CPG reservoir grids. At first, the CPG grid is mapped, in a reference space, into a non uniform Cartesian grid by minimising the mapping deformation. Then, a hybrid mesh is generated in this reference space using the previous method. Finally, this mesh is mapped back into the real space. This mesh can also be optimised with respect to the deformation metric between the real space and the reference one.<br>