Treffer: Towards an open-source landscape for 3-D CSEM modelling

Large-scale modelling of 3-D controlled-source electromagnetic (CSEM) surveys used to be feasible only for large companies and research consortia. This has changed over the last few years, and today there exists a selection of different open-source codes available to everyone. Using four different codes in the Python ecosystem, we perform simulations for increasingly complex models in a shallow marine setting. We first verify the computed fields with semi-analytical solutions for a simple layered model. Then we validate the responses of a more complex block model by comparing results obtained from each code. Finally, we compare the responses of a real-world model with results from the industry. On the one hand, these validations show that the open-source codes are able to compute comparable CSEM responses for challenging, large-scale models. On the other hand, they show many general and method-dependent problems that need to be faced for obtaining accurate results. Our comparison includes finite-element and finite-volume codes using structured rectilinear and octree meshes as well as unstructured tetrahedral meshes. Accurate responses can be obtained independently of the chosen method and the chosen mesh type. The runtime and memory requirements vary greatly based on the choice of iterative or direct solvers. However, we have found that much more time was spent on designing the mesh and setting up the simulations than running the actual computation. The challenging task is, irrespective of the chosen code, to appropriately discretize the model. We provide three models, each with their corresponding discretization and responses of four codes, which can be used for validation of new and existing codes. The collaboration of four code maintainers trying to achieve the same task brought in the end all four codes a significant step further. This includes improved meshing and interpolation capabilities, resulting in shorter runtimes for the same accuracy. We hope that thes
The work of DW was conducted within the Gitaro.JIM project funded through MarTERA, a European Union’s Horizon 2020 Framework Programme, grant agreement No. 728053. The development of custEM by RR as part of the DESMEX/DESMEX II projects was funded by the Germany Ministry for Education and Research (BMBF) in the framework of the research and development program Fona-r4 under grants 033R130D/033R130DN. The work of OC-R has received funding from the European Union’s Horizon 2020 Framework Programme under the Marie Sklodowska-Curie grant agreement No. 777778. Further, the development of PETGEM has received funding from the European Union’s Horizon 2020 Framework Programme, grant agreement No. 828947, and from the Mexican Department of Energy, CONACYT-SENER Hidrocarburos grant agreement No. B-S-69926. Furthermore, OC-R has been 65% cofinanced by the European Regional Development Fund (ERDF) through the Interreg V-A Spain-France-Andorra program (POCTEFA2014- 2020). POCTEFA aims to reinforce the economic and social integration of the French–Spanish–Andorran border. Its support is focused on developing economic, social and environmental crossborder activities through joint strategies favouring sustainable territorial development. The work of LH received funding from the National Science Foundation EarthCube program under award 1928406.
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