Multiple inversion scenarios for enhanced interpretation of marine CSEM data using iterative migration: A case study for the Shtokman gas field, Barents Sea

The integration of shared earth modeling and robust 3D CSEM modeling and inversion is the key to deriving a reliable quantitative interpretation from marine controlledsource electromagnetic (CSEM) data. Workflows should make use of all available subsurface data and enable the interpreter to select the most geologically relevant resistivity model from the multitude of models that satisfy the same CSEM data. To this end, we present our implementation of an iterative migration method for CSEM data, equivalent to rigorous inversion. Our iterative migration method is based on the 3D integral equation method with inhomogeneous background conductivity and focusing regularization with a priori terms. Here, we will show that focusing stabilizers recover more geologically realistic models with sharper geoelectric contrasts and boundaries than traditional smooth stabilizers. Additionally, we will show that focusing stabilizers have better convergence properties than smooth stabilizers. Our method is implemented in a fully parallelized code, which makes it practical to run large-scale 3D iterative migration on multi-component, multi-frequency and multi-line CSEM surveys for models with millions of cells. We present a suite of interpretations obtained from different migration scenarios for a 3D CSEM feasibility study computed from a detailed model of the Shtokman gas field in the Russian sector of the Barents Sea.