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Abstract: Petrolem Systems in the Austral Basin

J. Robbiano, H. Arbe

The aggressive exploration activities pursued over the past five years, both onshore and offshore, have contributed to increase our knowledge about how the Petroleum Systems functioned within the basin. Three main Petroleum Systems were identified, and referred to as Jurassic, Lower Cretaceous and Aptian-Tertiary Petroleum Systems.

The Jurassic P.S. is restricted to the volcanic, volcaniclastic and clastic sequences (known as Tobifera Series) related to the opening of the South Atlantic Ocean. Lacustrine to marine black shales give good source rock, locally developed; oil and gas, poorly developed, was trapped in fluvial to littoral sandstones, related to the same sedimentary cycle.

The Lower Cretaceous P.S. represents the main petroleum system of the Austral Basin, and it is related to the main oil and gas accumulations today known within the basin. The lateral relation between the marine source rocks (Palermo Aike, Inoceramus Inferior, Pampa Rincon Formations) and the continental to littoral Springhill Formation in a transgressive signature indicates the extent of the migration from the oil kitchen, in the present deep location of the basin, to the shallow eastern flank of the Austral Basin. The cumulative production and reserves of this efficient petroleum system are more than 400 MM of petroleum and gas equivalent.

The Aptian-Tertiary P.S. is related to the Margas Verdes source rock that has fed younger reservoirs which have developed since the Upper Cretaceous (?)-Palaeocene and could also feed Upper Oligocene sandstones, associated with lowstand system tracts. Commercial accumulations were tested in Campo Boleadoras and Maria Ines fields, towards the deepest zones of the Austral Basin. This petroleum system will figure prominently in exploration activities over the coming years, specifically in those areas where the main petroleum system is not laterally efficient.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela