Novel Algorithms for Modeling Sedimentation and Compaction using 3D Unstructured Meshes

In this paper, we discuss some novel techniques for modeling sedimentation and compaction using fully unstructured meshes. The numerical modeling of the sedimentation process is a critical part of basin simulation and synthetic stratigraphy modeling. Normally, structured curvilinear meshes are used to represent sedimentary sequences to be deposited during the simulation. Using this approach, 2D grids represent layers of newly deposited sediments of a sequence during the simulation. In simulations that involve compaction, the 3D meshes are restricted to have vertical planes parallel to depth direction in order to accommodate the compaction calculation since most compaction algorithms in basin modeling are essentially one-dimensional. This kind of curvilinear mesh poses severe limitations to represent complex geological structures such as non-vertical faults, pinch-outs and salt domes. Unstructured meshes are much more flexible for representing complex geometry. We have developed new algorithms to use arbitrarily defined unstructured meshes for modeling numerically sedimentation and compaction in 2D and 3D. These algorithms (1) allow the generation of stratigraphic meshes by solving the Laplace equation to generate isosurfaces representing time lines that constrain the triangulation and (2) use a Streamline Upwind Finite Element formulation (SUPG) to calculate compaction during the simulation of evolving sedimentary basins. These algorithms have being applied with success in a 3D multiphase fluid flow simulator that we are developing to handle complex geometries with distinct degrees of mesh refinement/resolution during the simulation.