A finite element multifrontal method for 3D CSEM modeling in the frequency domain

Abstract

There has been a recent increase in the use of controlled-source electromagnetic (CSEM) surveys in the exploration for oil and gas. We developed a modeling scheme for 3D CSEM modeling in the frequency domain. The electric field was decomposed in primary and secondary components to eliminate the singularity originated by the source term. The primary field was calculated using a closed form solution, and the secondary field was computed discretizing a second-order partial differential equation for the electric field with the edge finite element. The solution to the linear system of equations was obtained using a massive parallel multifrontal solver, because such solvers are robust for indefinite and ill-conditioned linear systems. Recent trends in parallel computing were investigated for their use in mitigating the computational overburden associated with the use of a direct solver, and of its feasibility for 3D CSEM forward modeling with the edge finite element. The computation of the primary field was parallelized, over the computational domain and the number of sources, using a hybrid model of parallelism. When using a direct solver, the attainment of multisource solutions was only competitive if the same factors are used to achieve a solution for multi right-hand sides. This aspect was also investigated using the presented methodology. We tested our proposed approach using 1D and 3D synthetic models, and they demonstrated that it is robust and suitable for 3D CSEM modeling using a distributed memory system. The codes could thus be used to help design new surveys, as well to estimate subsurface conductivities through the implementation of an appropriate inversion scheme.

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.…”

Modelling IP effects in airborne time domain electromagnetics

“…If iterative methods are employed, the response at each frequency can be calculated in parallel. This makes frequency domain methods efficient at solving problems with a limited number of sources, however, they quickly become computationally limiting as the number of sources grows (da Silva et al, 2012;Streich, 2009). …”

Three-dimensional parallel edge-based finite element modeling of electromagnetic data with field redatuming

“…In the recent years, the edge-based finite element method, which was originally introduced by Nédélec (1980), gained the interests of the geophysical community for 3D modeling of the EM fields (Silva et al, 2012;Cai et al, 2014). The edge element approach is characterized by better properties, such as automatic enforcement of tangential field continuity and divergence free condition, for the simulating of electromagnetic field compared to the conventional nodebased finite element method (Jin, 2002).…”