Evolution of a Submarine Channelised Fan System, Santos Basin, Brazil: Application of Loop-Scale Seismic Techniques and Integration with Fine-Scale Well Data
Despite a pay section in excess of 100m of high net-to-gross, multi-Darcy sand, there are considerable challenges for the development of BS-4 Atlanta, a Shell-operated heavy oil, Eocene deepwater discovery, Santos Basin, Brazil. Reprocessed 3D seismic data together with high quality image logs nevertheless provide a valuable dataset to better understand the architecture and facies of a channelized sand-rich turbidite system.
Loop-scale seismic evaluation involves volume interpretation and detecting subtle features using waveform classification. The current focus is on how heterogeneities at the log scale relate to seismic response. The analysis builds on previous work that established the regional context, paleo-slope position, and gross depositional architecture of the reservoirs.
The Atlanta reservoir complex is part of a channelized apron exceeding 600 km2 developed across an inherited stepped slope profile, which is ultimately related to thickness variations in Aptian salt. The apron is fed by several NW-SE oriented slope channels that become progressively younger towards the NE. At the base of the reservoir section, seismic interpretation reveals broad submarine channels with systematic migration patterns that are often seen in steeper slope channels, but unusual in such a low-gradient and sand-rich setting. These pass upward into more distributary channel and lobate forms. Wells show a corresponding split between lower, massive sands and an upper, more heterogeneous section characterized by the prevalence of thin shale-clast conglomerate layers within high quality sands. Depositional features are often more resolvable in the aquifer, away from well control. This suggests a decrease in net-to-gross, which enhances the seismic signature. Conversely, pore fluid changes complicate the interpretation in the field area.
The observations suggest that the system was overall strongly depositional, consisting of a limited number of largely aggradational channel and lobate elements. Integration of seismic interpretation with extensive image logs (FMI) and limited core data, provides a framework for understanding the distribution of key heterogeneities that could significantly impact reservoir performance. The results of this study are consistent with research developments in stratigraphic modeling, linked to outcrops, and as such provide general insights into static reservoir model construction in such systems.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009