We analyse a strategy to optimize the computational effort of large-scale electromagnetic (EM) modeling and particularly inversion, the latter usually requiring a large number of forward modeling solutions. While we are interested in finely gridded earth models to capture realistic structures, the forward modeling operator may act upon a coarser simulation grid, or a subsection of the model grid, thus providing significant potential for computational speed-up. After briefly outlining the methodology of the grid transfers and its implications on the inversion scheme, we demonstrate the method on a marine CSEM survey example.

The growing use of the controlled-source electromagnetic method (CSEM) for exploration applications has been driving the technical development of data acquisition, as well as three-dimensional (3D) modeling and imaging techniques. However, targeting increasingly complex geological environments also further enhances the problems inherent in large-scale inversion, such as non-uniqueness and resolution issues. In this paper, we report on two techniques to mitigate these problems. We use 3D joint CSEM and MT inversion to improve the model resolution. Further, a hybrid model parameterization approach is presented, where traditional cell-based model parameters are used simultaneously within a parametric inversion.