Abstract: The Petroleum Geology of the Sub-Andean Basins
Jeremy M. P. Mathalone
The sub-Andean trend of basins spans the entire length of South America from Venezuela in the north to Argentina in the south. All the basins produce hydrocarbons with the exception of the Argentinian Bolsones complex and the Peruvian Madro de Dios which is prospective but virtually unexplored. There have been some 119 billion barrels of oil and 190 TCF of gas discovered to date, comprising 93% of the continent's oil reserves.
The basins lie immediately east of the Andes mountain range and are mainly asymmetric Upper Tertiary, westerly dipping foreland basins that overlie a series of earlier Tertiary, Mesozoic and Paleozoic depocentres. All the basins have been compressively deformed as recently as the Upper Miocene, by the eastwards growth of the Andean Cordillera.
Giant oil and gas fields sourced from shales of varying age, have been found along the whole trend of basins, with an predominance of gas in the south. The rich marine Upper Cretaceous La Luna and equivalent shales of Venezuela, Colombia and Ecuador have been responsible for generating 86% of the hydrocarbons discovered to date in the sub-Andean basins. Proven sources include Devonian, Carboniferous, Permian and Triassic shales in the central area, comprising Peru, Bolivia and northern Argentina. In southern Argentina, oils have been sourced from Uppermost Jurassic and Lower Cretaceous marine and lacustrine shales.
Over 7500 wildcat wells have been drilled in basins along the trend, with a 15% success rate. Many of the basins are very lightly explored, with considerable potential for future discoveries.
AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela