Iterative electromagnetic migration for 3D inversion of marine controlled-source electromagnetic data

The key to deriving a reliable quantitative interpretation from marine controlledsource electromagnetic data is through the integration of shared earth modeling and robust 3D electromagnetic inversion. Subsurface uncertainty is minimized through efficient workflows that use all available subsurface data as a priori information and which permit multiple resistivity models to explain the same observed data. To this end, we present our implementation of an iterative migration method for controlledsource electromagnetic data that is equivalent to rigorous 3D inversion. Our iterative migration method is based on the 3D integral equation method with inhomogeneous background conductivity and focusing regularization with a priori terms. We will show that focusing stabilizers recover more geologically realistic models with sharper resistivity contrasts and boundaries than traditional smooth stabilizers. Additionally, focusing stabilizers have better convergence properties than smooth stabilizers. Finally, inhomogeneous background informationdescribed as a prioriresistivitymodels can improve the fidelity of the final models. Our method is implemented in a fully parallelized code. This makes it practical to run large-scale 3D iterative migration on multicomponent, multifrequency and multiline controlled-source electromagnetic surveys for 3D models with millions of cells. We present a suite of interpretations obtained from different iterative migration scenarios for a 3D controlled-source electromagnetic feasibility study computed from a detailed model of stacked anticline structures and reservoir units of the Shtokman gasfield in the Russian sector of the Barents Sea.