Geology Across Mid-Ocean Ridges – A Framework for Evaluating the South Atlantic Pre-Salt

Abstract

Continental margins have been the hunting ground of Oil and Gas companies for many decades. The development of deepwater drilling technology and improvements in subsurface imaging have enabled industry to push activity to more and more distal settings. In such settings, the formation history of continental margins becomes more and more important for a working hydrocarbon system. An example of this is the South Atlantic Pre-Salt, where shelfal activity targeting Tertiary reservoirs have made way for deep-water activity with Early Cretaceous, syn-rift objectives. The formation history of such distal continental margins has been a subject of significant research in recent years. The academic community has proposed numerous models to explain observations in distal settings and although there is general concensus that there are different “Crustal Domains”, the definitions used by authors vary considerably and the implications for a working petroleum system are not fully explained. To underpin Shell’s regional understanding of the South-Atlantic Pre-Salt petroleum system, we have defined a number of key mapping criteria on deep seismic reflection profiles (ION SPAN data) and magnetic datasets that help define and differentiate the various crustal domains. We utilized plate modeling software to analyze both sides of the Atlantic in a single framework and integrated all available observations of the Pre-Salt basin into one unified interpretation. The result is a single crustal domain interpretation over the entire South Atlantic Salt Basin, based on clearly defined mapping criteria. The various domains can subsequently be linked to elements of a working petroleum system (such as timing of structuration, heatflow history, expected stratigraphic sequence and depositional environment), which allows us to differentiate areas into different play-level risk profiles. We will show how this work reveals new insights into the opening of the Atlantic, how it highlights similarities on different sides of the Atlantic and that this framework enables us to differentiate opportunities in the pre-salt (such as in the Brazil bid-rounds) into different risk-profiles.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018