Subsalt Imaging Improvements in the Keathley Canyon Region of the Gulf of Mexico

The northern part of the Gulf of Mexico (GOM) has an active oil and gas industry presence, and formations in deep-water have become important targets due, in part, to advances in subsalt seismic imaging. Typically, the most prospective hydrocarbon reserves have been discovered around salt basins, but the complex overburden and salt geometries lead to challenges in subsalt imaging. In this case study, we aim to show the value of focusing on building robust low-wavenumber models that positively impact kinematics in the supra-salt region. These changes lead to improved imaging and geologic plausibility of the subsalt, especially at the Wilcox turbidite formation located at Lower Tertiary Trend in the deepwater GOM. The key to building a model best suited for imaging is to ensure the low-wavenumber model is carefully and diligently constructed to ensure the correct and robust supra-salt image. Once that is resolved, the deeper sections of the model can be built leveraging reflection energy in full waveform inversion (FWI) and with sub-salt tomography. The resulting reverse time migration (RTM) image provides better continuity of events, higher resolution, and simpler structure. In addition to the 30 Hz RTM generated at the end of the model-building process, a FWI-derived reflectivity (FDR) was generated using the final velocity model. The FDR utilized the full benefits of FWI, mainly illumination compensation and noise reduction, to provide a supplementary volume to the RTM image.