Pre-salt Imaging in Brazil’s Santos Basin Using a Variable-depth Streamer Data Set
Lanlois, Jeremy1 and Bai, Bing
Much attention has been given to the Santos Basin because of the impressive discoveries in the area; yet, because of the region’s geologic complexity, producing accurate pre-salt images can be challenging. We have recently seen a surge of unconventional acquisition configurations designed to acquire data with broader bandwidth. Because of its richer low-frequency content, which has stronger penetration into deep pre-salt targets, variable-depth streamer acquisition is an appealing technology to implement in the region. We examine a variable-depth streamer data set, to focus on modifications to SRME and deghosting.
Unlike conventional flat-streamer acquisition, the variable-depth streamer follows a survey-specific cable depth profile. The variations in cable depth create a diverse ghost response not seen in conventional acquisition, requiring modifications to the processing work flow. A pre-migration "bootstrap" approach (Wang 2012) to deghosting is used. The approach utilizes a mirror dataset generated from 1D ray tracing, and jointly inverts for the receiver-ghost-free data. To improve turnaround time, a new SRME flow is developed. Deghosting is done prior to the multiple-prediction in order for the predicted multiple to be ghost-free. The predicted multiple is then adaptively subtracted from the ghost-free input. With this flow a re-ghost step is unnecessary. Where post-migration deghosting methods (Soubaras 2010) require two migrations per model iteration, pre-migration deghosting improves the runtime by requiring just one migration. This creates opportunities to run additional tomography iterations and salt interpretation scenarios. The rich bandwidth associated with variable-depth streamer acquisition provides improved details in the sediment tomography and more accurate salt interpretations, providing an improved image.
We have shown the need for processing adjustments associated with variable-depth streamer data, including receiver deghosting and multiple-attenuation. The challenges associated with processing variable-depth streamer data are significant, but the potential for improved imaging make them worth the effort. We have shown, using real data examples from the Santos Basin, the benefits of increased low frequency signal penetration and broader bandwidth associated with variable-depth streamer acquisition.
AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013