Three-dimensional modelling of controlled-source electromagnetic surveys using an edge finite-element method with a direct solver

A fully three-dimensional finite-element algorithm has been developed for simulating controlled-source electromagnetic surveys. To exploit the advantages of geometric flexibility, frequency-domain Maxwell's equations of the secondary electric field were discretised using edge-based finite elements while the primary field was calculated analytically for a horizontally layered-earth model. The resulting system of equations for the secondary field was solved using a parallel version of direct solvers. The accuracy of the algorithm was successfully verified by comparisons with integral-equations and iterative solutions, and the applicability to models containing large conductivity contrasts was verified against published data. The advantages of geometry-conforming meshes have been demonstrated by comparing different mesh systems to simulate an inclined sheet model. A comparison of the performance between direct and iterative solvers demonstrated the superior efficiency of direct solvers, particularly for multisource problems.