Methods based on the implicit description of geometrical objects offer an efficient framework to quickly build complex structural models with the occurrence of faults and fractures. BRGM has been leading research on this field for many years with the development of the GeoModeller software (Lajaunie et al., 1997; Calcagno et al., 2008). Such frameworks are now implemented in other commercial off-the-shelf geomodeling software (e.g. Gocad-SKUA, Leapfrog…), yet the modeling of complex fault systems remains a challenging task. The approach chosen in GeoModeller is especially intuitive and powerful as fault slip is not prescribed but automatically deduced from available data. For example, it was used to build a 3D geological structural model of of the Bouillante geothermal field in Guadeloupe (Calcagno et al., 2012).

When it comes to produce conformable meshes of such complex geological models the implicit nature of surfaces make volume meshing a non-trivial task. The Computational Geometry Algorithms Library (CGAL) offers a powerful 3D mesh generation package dedicated to such implicit frameworks. It is based on successive Delaunay refinements with a mechanism protection to ensure a fair representation of sharp features, embedded in the mesh, and also to guarantee the termination of the refinement process, no matter the geometrical complexity. Courrioux et al. (2012) plugged these algorithms in the GeoModeller software that can produce conformal tetrahedral meshes that exactly match any geological object and its 2D geometrical boundaries (geological interfaces, faults…) or 1D sharp features (surfaces intersection…).