Analysis of 3D finite-element forward modeling of CSEM data using three different formulas and unstructured grids
ZHOU Feng1,2,3,4, ZHANG Zhiyong1,2, CHEN Huang3, TANG Jingtian3, DENG Juzhi1,2, LI Yong4
1. Fundamental Science on Radioactive Geology and Exploration Technology Laboratory, East China University of Technology, Nanchang, Jiangxi 330013, China; 2. School of Geophysics and Measurement-control Technology, East China University of Technology, Nanchang, Jiangxi 330013, China; 3. School of Geosciences and Info-physics, Central South University, Changsha, Hunan 410083, China; 4. Key Laboratory of Geophysical Electromagnetic Probing Technologies of Ministry of Natural Resources, Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang, Hebei 065000, China
Abstract:High-precision and efficient 3D CSEM forward modeling algorithms have always been one of the key and hot issues in the study of electromagnetic forward modeling. Currently, one electric field equation and two A-Φ coupling potential equations with different structures are often used to solve 3D CSEM forward modeling problems. In this paper, the application effects of these three equations were analyzed by a finite element method. Firstly, in view of the CSEM boundary value problem, an electric field equation and two A-Φ coupling potential equations with a curl-curl structure and a Laplacian structure, respectively, were derived. Secondly, for elimination of field source singularity, the computational regions were discretized with unstructured tetrahedral grids. A local refinement technique for the field source was also applied for an accurate solution to the unified field source integration. Lastly, the three equations were fast solved through a Krylov subspace iterative algorithm and the PARDISO solver. The correctness of the algorithms developed in this paper was verified by calculation of the electromagnetic responses of the magnetic dipole source and the electric dipole source via the three equations, respectively, with a homogeneous half-space geoelectric model. The convergence, memory consumption and solution accuracy of the three CSEM forward equations were analyzed with a geoelectric model of low-resistance anomalous bodies. The results show that within a small computational region, the electric field equation based on vector finite elements has higher solution accuracy and higher solution efficiency. Otherwise, the A-Φ coupling potential equation with a Laplacian structure is more suitable than the other two equations for 3D CSEM forward modeling studies.
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ZHOU Feng, ZHANG Zhiyong, CHEN Huang, TANG Jingtian, DENG Juzhi, LI Yong. Analysis of 3D finite-element forward modeling of CSEM data using three different formulas and unstructured grids. Oil Geophysical Prospecting, 2021, 56(5): 1190-1202.
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