Angle-Restricted FWI for Shallow Reservoir Characterisation

In the Barents Sea, bright amplitudes on seismic data below the Base Quaternary may indicate the presence of hydrocarbon reservoirs. To allow characterisation and quantitative interpretation of these potential reservoirs, analysis of amplitude versus reflection angle (AVA) information is crucial. Even with the availability of high-quality Q-Kirchhoff pre-stack depth migration (QPSDM) products, transmission-absorption relating to shallow gas pockets along with residual surface-related and interbed multiples may compromise the imaging of these shallow reservoirs. By using the full wavefield, imaging from full-waveform inversion (FWI Imaging) provides a reflectivity image without the need to perform the usual pre-processing and migration steps. While FWI Imaging has delivered superior results in terms of imaging compared to more conventional migration methods, it has so far only provided a structural image, without access to common image gathers used to derive AVA information. In this study, we extract elastic information from acoustic FWI Images, generated from impedance updates using angle-restricted raw seismic data. The results of the angle-restricted FWI flow provide comparable AVA products to those obtained from a conventional QPSDM approach and a cleaner and more structurally appropriate AVA image in areas with complex near-surface geology suffering from lack of resolution, noise content or absorption-transmission effects.