Using Broadband mCSEM-driven Velocity Model Building to Improve Complex Subsalt Imaging

We present the potential of broadband marine Controlled Source Electromagnetics (mCSEM) coupled with a Cooperative Interpretation Workflow (Resistivity-to-Velocity transform) to address the major critical steps in subsalt and around salt imaging, i.e. estimation of resistivities/velocities above the salt, definition of salt geometry and subsalt resistivity/velocity update.

The work presents estimates of the range of compressional velocity models derived from resistivity models computed from broadband mCSEM inversions. The approach is developed applying the Hacikoylu’s petrophysical cross-property relation and uncertainty analysis of the data and the model. A study is presented from an ultra-deep water area of the Espirito Santo Basin, offshore Brazil, where the presence of complex allochthonous salt structures makes around-salt and subsalt seismic depth imaging extremely challenging. The results show that this recipe yields a good estimate of velocity away from the available control point, imaging the allochthonous base of salt (BOS) shallower than that interpreted from legacy NAZ seismic. This provides a cost-effective additional data set that may be used for integrated analysis, input for Reverse Time Migration (RTM) and/or as a ’sufficiently accurate' starting model for Full Waveform Inversion (FWI).