Unlocking extra value from vintage WAZ data using EFWI and ERTM: a subsalt imaging case study in the GOA

Elastic full-waveform inversion (EFWI) and high-frequency EFWI Imaging have gained increasing popularity, primarily with ocean bottom node (OBN) data, in areas where strong velocity contrasts and associated elastic effects are present, such as the Gulf of America (GOA). However, when only vintage streamer data are available in such regions, either wide or narrow azimuth streamer (WAZ/NAZ) data, seismic processing remains largely limited to an acoustic framework, based on the hypothesis that elastic effects are less significant for streamer data with limited offsets. Through a subsalt imaging case study in the GOA, we demonstrate that even with WAZ data, processing within an elastic framework, comprising both EFWI and elastic reverse-time migration (ERTM), is needed to properly utilize the postcritical information of the input streamer data, which leads to imaging improvements in complex salt environments. To better understand the improvements observed from the elastic solution in field data, a synthetic study was conducted to illustrate the potential impact of strong elastic effects arising from the highly dipping salt-sediment interface in the overburden. The synthetic study shows that elastic effects can be recorded from near to far offsets within a typical streamer offset range. Therefore, improvements from the elastic solution can be observed across all offsets in the gather domain, which is consistent with the observations from field data. Moreover, high-frequency EFWI Imaging further unlocks the value of vintage WAZ data, providing images with better signal-to-noise ratio (S/N) and subsalt illumination compared to ERTM, particularly in challenging subsalt areas.