Tackling subsalt complexity with elastic FWI using long-offset, low-frequency sparse OBN data

In recent years, full-waveform inversion (FWI) techniques have evolved significantly - from acoustic FWI (AFWI) that works surprisingly well in salt environments to the latest elastic FWI (EFWI) and high-frequency EFWI Imaging that provides unprecedented clarity in subsalt imaging - largely driven by rapid advancements in algorithms and exponential increases in computing capacity. However, for salt and subsalt velocity updates in the Gulf of Mexico (GoM), poor low-frequency signal-to-noise ratio (S/N), lack of divingwave penetration, and uneven subsalt illumination still impede reliable subsalt imaging, even with state-of-the-art FWI algorithms. With a recently acquired long-offset, lowfrequency (LOLF) sparse ocean bottom node (OBN) data set, we successfully applied elastic Time-lag FWI (TLFWI) to invert subsalt velocity and generate a high-fidelity FWI Image. The survey utilized a Tuned Pulse Source (TPS) as the energy source, providing usable low-frequency signals down to ∼1 Hz. The combination of cutting-edge algorithm, innovative source design, and acquisition results in significant uplift in subsalt imaging in the structurally complex Garden Banks and Keathley Canyon (GB-KC) areas. Some key enhancements include redefined salt bodies, better delineation of over-pressure zones and mobile shales, and improved resolution of thin salt feeders and welds.