Monitoring presalt reservoirs with hybrid acquisitions and 4D FWI

Many fields in the Brazilian pre-salt have been historically imaged with narrow-azimuth towed-streamer (NATS) data and only recently have been surveyed with ocean bottom nodes (OBN). Some cases of time-lapse 4D seismic monitoring are limited to hybrid pairs of data, where a NATS baseline acquisition was performed before production start and an OBN data set was acquired later for monitoring. This leads to low repeatability, imposing many challenges for extracting reliable 4D signal, especially in the context of the subtle changes expected from pre-salt carbonate reservoirs. Considering this, we developed a novel joint 4D full-waveform inversion (FWI) formulation to attenuate the adverse effects of low repeatability due to diverse acquisition geometries. Results are demonstrated using field data from the Santos Basin, revealing potentially genuine 4D anomalies.