Top of salt impact on full waveform inversion sediment velocity update

Full waveform inversion usually fails to update the sediment velocity in close vicinity of the top of salt (TOS) because of the strong velocity contrast between the sediment and salt. This phenomenon is a common challenge in practice, and it is not yet well understood. We investigate the relationship between FWI’s sediment velocity update and the accuracy of the TOS. The results indicate that the initial model with inserted salt helps update the sediment model, and a more accurate TOS provides a better sediment velocity update. However, an accurate TOS is not available unless the sediment velocity, particularly right above the TOS, has been correctly updated. We therefore propose a workflow to obtain a reasonable TOS for the FWI sediment velocity update using iterative FWI and salt interpretation. Using 2D synthetic data and real data, we demonstrate that our workflow yields a better FWI update above the salt than compared to using the sediment model as the initial model.