Interpretation and De-Risking of Ultra-Deep Water Prospects in the SEAL Basin, Brazil, Using a Cognitive Interpretation Approach and High Integrity AVO Information

Abstract

In the current low oil price environment, seismic interpretation workflow innovation is essential to identify and de-risk exploration targets in ways that are faster than legacy methods yet honor the geology. This is even more valid and demonstrated by using a high integrity pre-stack broadband 3D seismic. In this study, a Cognitive Interpretation workflow was applied to reveal, interpret and de-risk exploration targets offshore Brazil, with a rapid project turnaround.

The PSDM dataset (pre-stack towed dual-sensor streamer seismic, MC3D BM-SEAL-10/11 courtesy of PGS) available covered over 4500km² of the Sergipe-Alagoas basin, and included full and angle stack reflectivity volumes. The targets were Upper Cretaceous turbidite sand accumulations such as Barra and Farfan, discovered in 2012 and 2013 respectively. Well log information for the Barra discovery well was also available.

Frequency decomposition and RGB blending, combined with stratigraphic slicing, clearly revealed the geomorphology of the depositional systems and crevasse splay nature of the Barra sand. An AVO effect at the discovery well was identified, and was supported by analysis of the logs and interpreted as a Class III AVA effect. Having correlated this seismic fluid response to the well information, the angle stack information was interpreted using an RGB blend combining near, mid and far magnitudes respectively. This highlighted zones in the dataset with a strong far amplitude signature in the blend, which allowed for rapid AVO reconnaissance. This critically revealed that the Barra accumulation was distinct from the channel systems that did not show an AVO response. The blend did however highlight another zone of strong far offset response, interpreted to represent the Farfan sand body. Finally, as the AVO blend represented a combination of fluid effect constrained by geomorphology, the Barra and Farfan anomalies were directly interpreted as 3D geobodies, with gross rock volumes estimated for both.

By combining the latest standards in seismic acquisition and processing, and marrying that to a modern seismic interpretation method, we were able to reveal, interpret and de-risk the accumulations in an ultra-deep water setting accurately in the space of just two weeks. This approach clearly demonstrated the benefits of using the highest quality data and interpretation methods, meeting the requirements of faster project turnaround, reduced risk, and no compromises on information quality.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018