Regularized and blocky 3D controlled source electromagnetic inversion

Since the interpretation of controlled source electromagnetic (CSEM) data proves challenging in complex geological settings, 3D CSEM anisotropic resistivity imaging problem is formulated as an inverse problem. A least-squares misfit functional is minimized with a quasi-Newton algorithm to cope with the large number of unknowns. Furthermore, model and data weights are applied to speed up the convergence of the non-linear inversion. A-priori information obtained for instance from seismic interpretation can be included either in a blocky inversion, i.e., where the resistivity cube is parameterized with a small number of parameters or with a regularized inversion. Since earth resistivity contrasts can be high and spatially well defined, minimum norm support regularization terms are implemented. Although the blocky inversion proves quite powerful, we show that results can be misleading in complex geological settings. A combination of the blocky and regularized inversions may provide a more robust approach to interpret CSEM imaging results. We illustrate this with a deep-water example.