Long offset ocean bottom node FWI and multi-azimuth tomography for high-resolution VMB

Efficient acquisition of large-scale, azimuth-rich ocean bottom node (OBN) data, with long offsets and high fold is now a reality. Such data provide an opportunity to apply advanced model building techniques to derive high resolution velocity models. As offsets increase the risk increases of cycle skipping and other instabilities being introduced into the model. Here, an iterative diving-wave full waveform inversion (DWFWI) workflow is used to provide stable, detailed model updates for OBN data. The technique is demonstrated on long offset OBN data from the Utsira High in the North Sea. We show that by making use of long offsets we can resolve the velocity model using DWFWI with confidence in the frequency range of 2-8 Hz. The process of progressively increasing the offset in DWFWI allows stable velocity model updates and can model sand injectites, shallow gas anomalies and deep geological structures. The model is then updated with multiazimuth tomography.