About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

Houston Geological Society Bulletin


Houston Geological Society Bulletin, Volume 52, No. 6, February 15, 2010. Pages 13 and 15.

Abstract: Lacustrine and Marine Pre-Salt Clastic and Carbonates Of Brazil and West Africa: Drivers for Reservoir Quality, Environoments Of Deposition and Analogs

Scott E. Thornton1, Nicholas B. Harris2, Ann-Marie Scott3, and Michael Dyer4
1Department of Geology and Geophysics, The University of Sydney and DI International
2Department of Geology, University of Alberta, Edmonton
3Roc Oil Company Limited
4DI International

Recent discoveries, past exploration and ongoing exploration in pre-salt, lacustrine and marine reservoirs in Brazil and Angola have often encountered mindboggling complexity in both carbonates and clastics. The key to reaching an enlightened understanding of this complexity relies more on creative right brain thinking than left brain logic and data collecting. Discoveries made in the last several years have challenged our depositional models and the dogma that the carbonates and clastics in the pre-salt of Brazil and Angola are plagued by poor reservoir continuity and quality. In fact, the reservoir quality of the pre-salt, microbial limestone reservoirs in the Tupi-Jupiter cluster of fields displays outstanding reservoir quality. The reservoir distribution and reservoir properties are a function of the depositional environment in large and small rift lakes as well as broad, apparently marine transgressive systems in the early Cretaceous. Carbonate and clastic reservoir distribution and quality in lakes and marine sag basins pre-salt are controlled by rift geometry and orientation, lake or ocean depth and cross-section profile, wave climate and fetch, drainage patterns in the hinterland, entry points of clastics, lake salinity, local climate and cycles of lake level fluctuation. These drivers for understanding reservoir quality and continuity will be reviewed on first principles from our knowledge of recent and ancient deposits, as well as theoretical framing. Field analogs and regional data will be reviewed for the Santos and Campos basins of Brazil as well as the Kwanza and Cabinda basins of Angola. Our global analog set for clastic and carbonate reservoirs is really diverse in the aforementioned drivers, so that no two lacustrine, pore-salt basins are really alike. Our analog set for both Recent and ancient lakes is also not as statistically significant as sets for other reservoirs. Indeed, the microbial carbonate reservoirs being discovered in the pre-salt of the Santos Basin are likely marine, not lacustrine carbonates, deposited like other stromatolites. Computer-driven global climate models for lakes in the present and past are much more difficult than those for marine and deltaic depositional environments and have had limited success. An enlightened and more successful exploration campaign in these high-potential reservoirs will result from the understanding of these first principles. Exploration campaigns driven by only seismic interpretation and structural modeling may be prone to a lower rate of success if not tempered by a more sophisticated understanding of the drivers for these complex and often excellent reservoirs.

Jupiter Discovery in Santos Basin, Brazil with Pre-Salt Sequences.

West African Time Line with Pre-Salt Sequences.

Copyright © 2010 by Houston Geological Society. All rights reserved.