A tetrahedral mesh generation approach for 3D marine controlled-source electromagnetic modeling

• Published in: Computers & geosciences Vol. 100; pp. 1 - 9
• Main Authors: Um, Evan Schankee, Kim, Seung-Sep, Fu, Haohuan
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.03.2017
• Subjects: Finite element modeling; Marine electromagnetic geophysics; Parallel computing; Marine electromagnetic geophysics; Parallel computing; Finite element modeling
• ISSN: 0098-3004; 1873-7803
• DOI: 10.1016/j.cageo.2016.11.007

3D finite-element (FE) mesh generation is a major hurdle for marine controlled-source electromagnetic (CSEM) modeling. In this paper, we present a FE discretization operator (FEDO) that automatically converts a 3D finite-difference (FD) model into reliable and efficient tetrahedral FE meshes for CSEM modeling. FEDO sets up wireframes of a background seabed model that precisely honors the seafloor topography. The wireframes are then partitioned into multiple regions. Outer regions of the wireframes are discretized with coarse tetrahedral elements whose maximum size is as large as a skin depth of the regions. We demonstrate that such coarse meshes can produce accurate FE solutions because numerical dispersion errors of tetrahedral meshes do not accumulate but oscillates. In contrast, central regions of the wireframes are discretized with fine tetrahedral elements to describe complex geology in detail. The conductivity distribution is mapped from FD to FE meshes in a volume-averaged sense. To avoid excessive mesh refinement around receivers, we introduce an effective receiver size. Major advantages of FEDO are summarized as follow. First, FEDO automatically generates reliable and economic tetrahedral FE meshes without adaptive meshing or interactive CAD workflows. Second, FEDO produces FE meshes that precisely honor the boundaries of the seafloor topography. Third, FEDO derives multiple sets of FE meshes from a given FD model. Each FE mesh is optimized for a different set of sources and receivers and is fed to a subgroup of processors on a parallel computer. This divide and conquer approach improves the parallel scalability of the FE solution. Both accuracy and effectiveness of FEDO are demonstrated with various CSEM examples. •Automatic, accurate and efficient tetrahedral mesh generation for 3D marine controlled source electromagnetic (CSEM) modeling.•Numerical dispersion analysis of tetrahedral meshes in the electromagnetic diffusion domain.•Relaxing excessive mesh refinement around receivers by introducing an effective receiver size.•Accelerating marine CSEM modeling with many sources on a parallel computer by constructing many small sub CSEM meshes.