3D multinary inversion of CSEM data based on finite element method with unstructured mesh

In controlled-source electromagnetic (CSEM) inversion with conventional regularization, the reconstructed conductivity image is usually blurry and only has limited resolution. To effectively obtain more compact conductivity models, we apply the concept of multinary transformation to CSEM inversion based on the finite element (FE) method with unstructured tetrahedral mesh. Within the framework of multinary inversion, the model conductivities are only allowed to be clustered within the designed values which is usually obtained from other a priori information or the conventional inversion. The synthetic studies show that the multinary inversion produces conductivity images with clearer model boundaries comparing to both the maximum smoothness inversion and the focusing inversion for realistic geoelectric models. We further applied the developed method to a land CSEM survey for mineral exploration. The multinary inversion results are closer to the ground truth comparing to the conventional maximum smoothness inversion and the focusing inversion. The developed method and numerical algorithm provide a new approach and workflow for CSEM inversion when the models need to have clear boundaries and clustering model values. Such geoelectric models could be very useful for geological interpretation in oil and mineral exploration when the a priori information (such as the estimated conductivity values) of the exploration targets is known.