Study Of 2.5D Isoparametric Finite-element Numerical Simulation Of Controlled-source Electromagnetic

In this paper, a data processing method is developed to calculate frequency-domain electromagnetic responses caused by a dipole source over a 2-D structure.The y-direction is set to be the strike direction, and the topographic relief,conductivity, dielectric permittivity, and magnetic permeability are invariantalong the y-axis, varying only in the x-z plane. An electric or magnetic dipolesource can be located anywhere. This is so-called 2.5-D forward modeling. As the major geophysics effective prospecting means, controlled-sourceelectromagnetic (CSEM) methods provide the opportunity to acquire high qualityelectromagnetic(EM) data in a short time. In modeling controlled-sourceelectromagnetic data, it is usual to separate the electromagnetic field into aprimary(background) and a secondary(scattered) field to avoid a sourcesingularity, and only the secondary field caused by anomalous bodies iscomputed numerically. However, this conventional scheme is not effective forcomplex structures lacking a simple background structure. So it is difficult tomodel realistic 2-D or 3-D structures and a finite source. Moreover, topographyalso must be considered in field surveys. Therefore, the present modeling method uses a pseudo-delta function todistribute the dipole source current, and does not need the separation of theprimary and the secondary field. In addition, the method employs anisoparametric finite-element technique to represent realistic topography andcomplex structures. Higher order interpolation functions are applied to calculatethe space derivative accurately in the finite-element equations.This data method is only the case of frequency-domain electromagneticresponses. In the case of time-domain electromagnetic responses, the Fouriertransform can be applied to transform it to frequency-domain electromagneticresponses then do as the same.