High frequency refraction/ reflection full-waveform inversion case study from North West Shelf offshore Australia

Abstract

The robustness of diving wave Full-Waveform Inversion (FWI) has been proven in industry, but the effectiveness is limited by its penetration depth. To target deeper reservoirs, therefore, requires the application of reflection FWI. This paper presents a real data 25Hz VTI FWI case study from North-West Shelf (NWS) Australia utilizing full wave-field. Starting from a high-quality reflection tomography VTI model, a top-down approach has been adopted. Diving wave FWI updates the shallow, then reflection FWI is introduced to further update the deeper section. The updated FWI model demonstrates significant uplifts in resolution and consistency with the geology. Two promising aspects can be observed: (1) the fairly solid uplifts in mitigating the imaging challenges: FWI reduces wave-field distortions, leads to overall improved focusing, gather flatness, continuity, and better positioning in depth; and (2) uncovers geological features beyond imaging: high-resolution FWI delineates small shallow anomalies and velocity boundaries across faults, and reveals the strong acoustic impedance contrasts at reservoir level. It demonstrates FWI can aid both in reducing the velocity uncertainty as well as providing a geological interpretation.