| Popis: |
Multiple geologic elements combine in the presalt section of deep-water Santos Basin, forming a quite unique exploration play: prolific and mature source rocks are present, synrift structures include huge intrabasinal highs, and the overlying evaporite seal extends throughout most of the area. Significant uncertainties related to reservoir presence and deliverability, which still persist as the key risks on this emerging presalt play, have been progressively reduced throughout a continued drilling campaign, which started in 2006. The most prominent and extensive intrabasinal high in the region is the Outer High of Santos Basin, a regional basement structure that forms a 12,000 km2 (4633 mi2) four-way closure at the Aptian level. The geologic history of the Outer High involves multiepisodic uplift and erosion of a series of rift fault-block shoulders during the Barremian. At that time, regional uplift resulted from a failed sea-floor spreading process that emplaced proto-oceanic crust in the southern Santos Basin. Concurrently, magmatic underplating is postulated as the mechanism responsible for locally thickening the crust and isostatically holding the Outer High as a present-day positive feature above its surroundings. Because of the extreme extension of the continental crust in Santos Basin, zones of deep crustal, or even upper mantle exhumation, are also expected near the transition from continental to oceanic crust. Before continental breakup, the Outer High was roughly located 200 km (124 mi) away from both the African and Brazilian hinge lines. This distal setting, coupled with a positive relief, limited siliciclastic input from the margins. The presence of a long-lived paleohigh, in such a clastic-starved environment, favored the development of a broad carbonate platform, during the Lower Aptian. Tectonically controlled water-level fluctuations affected the evolving platform, serving an important function on reservoir facies development. The Outer High has been the core region of a deep-water presalt exploration outbreak, after a pioneering drilling campaign that started around the middle of this decade. The hydrocarbon potential of this vast frontier area is yet to be fully unraveled. |
