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The Punta del Este Half Grabens, Offshore Uruguay: The Next Exploration Frontier in the South Atlantic


The South Atlantic opening is characterized by an initial extensional phase dominated by asymmetric half-grabens and identified, from south to north, in the North Falkland/Malvinas basin, Punta del Este (PdE) basin and Santos basin. Flanked by the world class pre-salt fields of Santos basin (Tupi, Jupiter, Carioca, Iracema, Iara among others) to the north and the recent discoveries in the North Falkland / Malvinas basin (Sea Lion, Zebedee, Isobel Deep) to the south, the PdE half grabens in offshore Uruguay emerge as the new frontier exploration along the South American margin of the South Atlantic. Recently acquired seismic allowed to refine the asymmetric configuration of these NW-SE - oriented rifts in the PdE basin, a common feature with the pre-salt half grabens in offshore Brazil and the North Falkland / Malvinas basin. It also helped to identify synrift and laterally extensive postrift (sag) sections. This configuration has the potential for stratigraphic and/or combined onlap / pinchout traps at the synrift and sag levels on the flexural margin, similar to several presalt traps, and also stratigraphic traps with synrift, turbidite reservoirs like in the Sea Lion discovery. Landward dipping master border faults present in the PdE half grabens, opposite to the present deepening of the continental margin, enhance trap integrity of structural (four-way) closures. This is due to the critical role played by differential compaction at the half-graben border fault margin to accentuate and/or create counter-regional dips necessary to form structural traps at the overlying sag level. The North Falkland / Malvinas basin could be a good analog for source rock presence in the PdE half grabens. It contains a late Jurassic (Tithonian) to early Cretaceous lacustrine source rock in the syn-rift section and an early post-rift (sag) section, of early Cretaceous (Valanginian to Barremian or Aptian) age. The Sea Lion discovery contains waxy oil in Lower Cretaceous, base-of-slope to basin-floor fan sandstone reservoirs. Overlying early post-rift immature source rocks acted as a seal. Additional potential could come from Permian sandstone reservoirs, where light oil (39° API) was found in the Cruz del Sur x-1 well in the Colorado basin, south of the PdE basin. Permian sediments with oil and gas inclusions were recently identified in the pre-rift basement of the PdE basin in the Gaviotin-1 well.