Broadband and ultra-long offset mCSEM - A recipe for complex subsalt imaging

We present the results of a demonstration research multi- component, ultra-long offset, broadband marine Controlled Source Electromagnetic (mCSEM) survey that was carried out over selected ultra-deep water area of the Espirito Santo Basin (offshore Brazil), where the presence of allochthonous salt structures makes around-salt and subsalt seismic depth imaging extremely challenging. We explain the workflows that we developed to combine and exploit the additional information that ultra-long offset, broadband mCSEM may provide to define and constrain ultra-deep water complex allochthonous salt geometries and salt, around-salt, subsalt multi-properties distribution such as the ones encountered in the Espirito Santo Basin and thus improve the seismic imaging through an enhanced velocity model and novel velocity model building. We show that the reconstructed resistivities, velocities and shapes of regions of interest are consistent with both the EM and the seismic data and that considerable improvement in resolution and speed is achieved compared to the current state-of-the-art. The results presented falsify the allochthonous base of salt (BOS) interpreted from NAZ seismic and hence providing an additional data set, that can be used as a cost-effective solution for integrated analysis, input for Reverse Time Migration (RTM) or as a starting point for Full Waveform Inversion (FWI).