Fast and accurate three‐dimensional controlled source electromagnetic modelling^†

Abstract

A B S T R A C TWe present a fast approximate method for three-dimensional low frequency controlled source electro-magnetic modeling. We apply the method to a synthetic model in a typical marine controlled source electromagnetic scenario, where conductivity and permittivity are different from the known background medium. For 3D configurations, fast computational methods are relevant for both forward and inverse modelling studies. Since this problem involves a large number of unknowns, it has to be solved efficiently to obtain results in a timely manner, without compromising accuracy. For this reason, the Born approximation, extended Born approximation and iterative extended Born approximation are implemented and compared with the full solution of the conjugate gradient fast Fourier transformation method. These methods are based on an electric field domain integral equation formulation. It is shown here how well the iterative extended Born approximation method performs in terms of both accuracy and speed with different configurations and different source positions. The improved accuracy comes at virtually no additional computational cost. With the help of this method, it is now possible to perform sensitivity analysis using 3D modelling in a timely manner, which is vital for controlled source electromagnetic applications. For forward modeling the solution at the sea-bottom is of interest, because that is where the receivers are usually located. For inverse modeling, the accuracy of the solution in the target zone is important to obtain reasonably accurate conductivity values from the inversion using this approximate solution method. Our modelling studies show that the iterative extended Born approximation method is fast and accurate for both forward and inverse modelling. Sensitivity analysis as a function of the source position and different reservoir sizes validate the accuracy of the iterative extended Born approximation.

Electromagnetic field analysis in the marine CSEM detection of homogeneous and inhomogeneous hydrocarbon 3D reservoirs

“…The latest research papers have considered only the responses from the solid (homogeneous) reservoir models with isotropic (Abubakar et al, 2009;Constable and Weiss, 2006;Da Silva et al, 2012;Kang et al, 2012;Key and Ovall, 2011;Løseth et al, 2008;Myer et al, 2012;Ray and Key, 2012;Sasaki, 2011;Schwarzbach et al, 2011;Tehrani and Slob, 2010;Weiss and Constable, 2006) or anisotropic (Brown et al, 2012;Li and Dai, 2011;Ramananjaona et al, 2011;Wiik et al, 2011) resistivity.…”

“…In the paper (Abubakar et al, 2009), the 2D reservoirs of a polygonal rather than rectangular shape were considered; but still they were considered as homogeneous. In the paper (Tehrani and Slob, 2010), the responses from a single and two separated reservoirs were compared. The biggest response was observed when the source was located above the edge of the reservoir.…”

Green's Tensors for the Diffusive Electric Field in a Vti Half-Space

“…Solutions for the two half spaces configuration are of interest in electric field integral equation solutions and approximations thereof [4][5][6][7][8]. Such solutions are also important for modeling by local methods such as finite-difference, finite-element and finitevolume methods [9][10][11][12] as well as for inversion methods based on local forward-modeling schemes [13][14][15][16].…”