The Brazilian oil exploration frontier has changed from simple post-salt targets to deeper and more complex pre-salt targets. This new exploration scenario mostly focuses on Santos Basin, southeast Brazil, where prospects generally lie beneath complex salt bodies with canopy overhangs and salt stratification. In such regions, conventional narrow-azimuth towed-streamer (NATS) data often fails to produce an image that can adequately de-risk prospects in the exploration phase. Ocean bottom node (OBN) data, on the other hand, is known to improve seismic velocity model building and imaging over production fields. Velocity models and corresponding imaging after full-waveform inversion (FWI) are much improved when used with OBN data, which features highquality low frequency content, longer offsets, and full azimuthal coverage. Those are crucial ingredients for deep and complex targets. Unfortunately, OBN data are not commonly available at the beginning of the exploration cycle, when uncertainty and risk are high. To reduce exploration risk in Santos Basin, we studied deploying sparse nodes on an exploratory scale. Using a decimated field OBN data set from Santos Basin, we show that the sparse node acquisition provides enough information for a reliable inversion with FWI. This velocity model can then be paired with conventional NATS data to yield an image with more accurate positioning of subsurface structures. Moreover, the sparse node data itself can also be used for imaging; we demonstrated that it contains valuable information about the pre-salt formations. Finally, we combined conventional NATS data and sparse nodes acquisition data in a least-squares framework, producing a structural image that can potentially further reduce risks at the exploration phase. We also derived a metric that aims to quantify the quality of the resulting seismic images.
Note: This paper was accepted into the Technical Program but was not presented at the 2020 SEG Annual Meeting.
