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Attribute Analysis and Morphologic Evaluation of an Incised Valley System in the Santos Basin, Brazil

Abstract

The Santos Basin offshore Brazil developed recently into one of the world’s most prolific hydrocarbon provinces and garners international attention due to significant pre-salt discoveries. Recent reprocessing of a 34,000 km2 regional dataset has delivered a high-resolution broadband 3D Kirchhoff pre-stack depth migrated stack, benefiting from state-of-the-art processing and model building technology, which facilitated an attribute analysis and morphologic evaluation of a subaquatic incised valley located on a paleo shelf break. The aim of this analysis was to assess the reservoir potential of sediment accumulations within this system as there are similar confined deep water channel complexes offshore West Africa with proven reservoirs.

Detailed mapping of the outer erosional valley boundary revealed several terrace features, stepping down towards the center of the valley, which indicate it was formed by multiple stages of fluvial incision carving into the formations below. Volume attributes such as amplitude, curvature, coherence, and spectral decomposition, were employed to analyze internal architectural elements and signatures of the deposits filling the valley. Analysis revealed buried channels and mass wasting events that are otherwise indistinguishable with legacy seismic volumes and traditional workflows. Utilizing seismic stratigraphic techniques, a morphological evaluation of the system led to the identification of seven depositional units of valley infill. These individual units were then described in detail to determine possible lithologic composition. Ultimately, each depositional unit within the system was determined to be dominated by shale-rich deposits and lacked significant coarse-grained sediment accumulations that characterize high quality reservoir sands.