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

  • da Silva N
  • Morgan J
  • MacGregor L
 et al. 
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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 de- composed 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 differen- tial 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 sol- vers 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 computa- tion of the primary field was parallelized, over the computa- tional 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 methodol- ogy. 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.

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Authors

  • Nuno Vieira da Silva

  • Joanna V. Morgan

  • Lucy MacGregor

  • Mike Warner

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