Integral equation method for 3D modeling of electromagnetic fields in complex structures with inhomogeneous background conduct ivity

their famous papers on the IE method . Many more researchers have me thod for three -dimensional (3D) electromagnetic (EM) contributed to the improvement and development of this method in modelin g in complex structures with inhomogeneous back­ recent yea rs (e.g., Wannamaker, 199 1; Dmitriev and Nesmeyanova, ground conductivity (1Be). Thi s method ove rcomes the stan­ 1992; Xiong, 1992; Xiong and Kirsch. 1992; Singer and Fainberg, dard limitat ion of the conventional IE method related to the 1997; Avdeev et al., 2002; Hursan and Zhdanov, 2002; Zhdanov, use of a horizon tally layered backgrou nd only. The new 3D 2002; Singer et aI., 2003; Abubakar and van der Berg, 2004 ; Avdeev, IE EM mode ling method still emp loys the Gree n's functions 2005; Yoshioka and Zhd anov, 2(05). for a horizon tally laye red ID model. However, the new meth ­ In the framework of the IE method, the conductivity distribution od allows us to use an inhomogene ous backgrou nd with the is divided into two parts: (I ) the background conductivity CTb, whic h IE method. We also introd uce an approac h for accuracy con­ is used for the Green 's functions calculation , and (2) the anomalous tro l of the IBC IE method. This new approach provides us conductivity D,CTa within the domain of integration D. It was empha­ with the ability to improve the accur acy of computat ions by sized in the original paper by Dmit riev (1969) that the main limita­ appl ying the IBC technique iterativ ely. Thi s approach seems tion of the IE method is that the background conductivity model to be extremely useful in computing EM data for multipl e must have a simple structure to allow for an effic ient Green 's func­ geolog ic mode ls with some com mon geoelectrical fea tures, tion calcul ation . The most widely used background models in EM like terrain, bathymetry, or other known structures . It may exploration are those formed by hor izontally homogeneous layers. find wide appl ication in an inverse prob lem solution, where The theory of the Green's funct ions for layered one-dimensional we have to keep some known geo logic structures unchan ged (I D) models is very well developed and lays the founda tion for effi­ durin g the iterat ive inversion . The method was carefully test ­ cient numerical algor ithms. Any devi ation from this ID background ed for modeling the EM field for compl ex struct ures with a model must be treated as an anomalous conductivity. know n variable background conductivity. The effectiv eness In some practical applica tions, however, it is difficul t to desc ribe a of this approa ch is illustrated by mode ling marine controlled ­ model using horizontally layered background co nductiv ity. As a re ­ source electromagnetic (MCSEM) data in the area of Gemini sult, the domain of integration may become too large, which increas­ Prospect, Gul f of Mexico . es significantly the size of the mode ling domain and of the requ ired