3D controlled source electromagnetic inversion with topography in the frequency domain
Zhu Cheng1, Li Tonglin2, Yang Haibin3, Liu Yongliang2, Wu Liang4, Hu Yingcai5
1. Minmetals Exploration and Development Co. LTD, Beijing 100010, China;
2. School of Geo-Exploration Science & Technology, Jilin University, Changchun, Jilin 130000, China;
3. Department of Geosciences and Natural Resource Management, University of Copenhagen, Denmark, DK1350, Denmark;
4. Changjiang Engineering Geophysical Prospecting Company, Wuhan, Hubei 430010, China;
5. Beijing Research Institute of Uranium Geology, Beijing 100029, China
Abstract：Seismic exploration is sometimes unsuccessful in some areas with difficult geological and topographical conditions such as complex mountainous area. Experiments show that the joint application with seismic and non-seismic methods especially electromagnetic (EM) is an effective way to ensure high quality prospecting. This paper discusses the theory and algorithm of three dimensional forward modeling and inversion of controlled-source electromagnetic method (CSEM) with topography, which is tested to be accurate in theoretical data inversion. The paper consists of two parts:3D forward modeling and non-linear conjugate gradient (NLCG) inversion. For 3D forward modeling, the finite difference based on scattered fields is implemented, and the obtained apparent resistivity in far field is similar with that of magnetolluric (MT) method on a typical model. Therefore the forward modeling algorithm is suitable and accurate. On the other hand, NLCG is used in the 3D inversion and initial solution optimization is adopted, which can efficiently reduce computation time consumption. Numerical experiments illustrate that the distribution of anomalous bodies can be well recovered by the proposed inversion and the initial solution optimization can dramatically reduce computation time consumption.
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