Revealing the subsalt in Garden Banks with a sparsely-shot TPS OBN and FWI
Michael Merritt, Guido Baeten, Vishram Rambaran, K. E. Godfrey, Kevin J. Bianchini, Tara Brothers, F. Chelminski, Alex Hao, Huawei Gao, Yumeng Su, Zhi-Yuan Wei
Abstract
The Garden Banks protraction area features some of the most complex geological features in the Gulf of Mexico (GOM), presenting tremendous challenges for subsalt imaging and exploration. Existing streamer seismic, characterized by offsets up to 15 km and poor low-frequency (LF) signal-to-noise ratio (S/N), has not proven effective on its own for subsalt velocity model building with full-waveform inversion (FWI) and imaging. To unlock subsalt exploration in this challenging area, Shell acquired a long-offset (∼60 km) sparse ocean bottom node (OBN) survey paired with a game-changing marine source to prioritize LF S/N, the Tuned Pulse Source (TPSTM). While the first full-scale use of this innovative new source, the entire survey was completed successfully with rich LF content visible down to ∼1 Hz, enabling FWI to correct large velocity model errors and create a LF image of the subsurface in record-time, all the way into basement. Despite having very sparse shots, the OBN images/velocities spectacularly reveal complicated subsalt structure, including salt feeders, shale bodies, and basement faulting. This resounding success not only demonstrates the feasibility of FWI with TPS OBN data; it also marks a significant, repeatable advancement in marine seismic sources for subsalt exploration.