Improving subsalt reservoir imaging with Reflection FWI: An OBN case study at Conger field, Gulf of Mexico

Reservoir imaging under the triangular Conger salt remains very challenging even after significant velocity model building efforts in recent years. Continuity and focusing of reservoir reflectors are sub-optimal due to the subtle velocity errors from the Conger salt and its neighboring carapace, which are very difficult for conventional methods, such as interpretation-guided salt scenarios and ray-based tomography, to resolve. Diving-wave full-waveform inversion (FWI) has difficulty updating the velocity at this depth due to the limit of maximum offset, and thus penetration depth, of input data. In this study, we performed reflection FWI (RFWI) using ocean-bottom node (OBN) data for velocity model updates. Our results showed that RFWI can effectively resolve the subtle low-wavenumber velocity errors in the overburden and substantially improve reservoir imaging. We also demonstrated that RFWI using OBN data can result in a better model than using wide-azimuth towed-streamer data due to its full azimuth and much longer offset coverage.