Geological Team No.293
Geological Team No.293
Li Y.,Hefei University of Technology |
Li Y.,Chinese Academy of Geological Sciences |
Li Y.,Laboratory of Geophysical Electromagnetic Probing Technologies |
Wu X.-P.,Hefei University of Technology |
And 7 more authors.
Chinese Journal of Geophysics (Acta Geophysica Sinica) | Year: 2017
Arrangement of underground media fractures, preferred orientation of mineral grains and mineral composition bedding stratification are the factors leading to anisotropy of electrical conductivity for submarine layers. It has been proved by many researches that the influence of conductivity anisotropy should not be ignored, because it may result in false geological structures in marine electromagnetic data explanation. Up to now, most of available methods used in three-dimensional (3D) modeling of marine controlled-source electromagnetism (MCSEM) are based on the theory of isotropic media, which cannot simulate MCSEM response in real submarine anisotropic layers. In this paper, the MCSEM boundary value problem for the secondary electric field in 3D anisotropic media is put forward. Its corresponding variational equation is derived and then solved with the vector finite element method, in which a rectangular mesh is applied to dissect the computational region and the field component is defined on the edge of the rectangular element. Consequently, a vector finite element method for 3D MCSEM modeling is developed to calculate electromagnetic response in arbitrary anisotropic media. Meanwhile, secondary field formulation is used to remove source singularity. Our vector finite element method is able to deal with the discontinuity of the normal component of the electric field in 3D anisotropic media, and the vector basis functions are divergence-free which avoids the spurious solution, showing obvious advantage over the traditional nodal finite element method. The comparison between the analytical and numerical solutions of a layered anisotropic model shows high accuracy of our algorithm with less than one percent of relative error. The numerical solutions from our 3D vector finite element modeling also match well with the results from an available 2D unstructured finite element method for a 2D anisotropic conductivity model. A three-dimensional model is then simulated which shows that the principal axis anisotropy of the conductivity and Euler angle have significant impact on Inline and Broadside electromagnetic responses. © 2017, Science Press. All right reserved.