South American Petroleum Geology - An Overview

Jeremy M. P. Mathalone

South America has been producing oil since the last century, with discoveries having been made in the majority of countries over 70 years ago.

The continent can simplistically be considered as five broadly north-south oriented provinces comprising the forearc basins of the west coast and the Andes mountain range with associated sub-Andean foreland basins immediately east. An interior shield area is punctuated with a series of Paleozoic sag basins and finally, the east coast is rimmed with passive margin (and rift) basins.

Over 10,000 wildcat wells have discovered some 125 billion barrels of oil and 184 trillion cubic feet of gas, nearly all from the sub-Andean trend of basins (116 billion barrels), itself dominated by Venezuela which has almost three quarters of the oil discovered on the continent to date. Giant hydrocarbon accumulations however, are present in nearly every other country on the trend. Most sub-Andean oil is sourced from Cretaceous marine shales.

On the other side of the continent, 7.5 billion barrels of oil have been discovered in the passive margin and rift basins of coastal Brazil. This oil is nearly all sourced by Cretaceous pre-rift lacustrine shales.

The west coast, Andes and shield basins have seen few hydrocarbon discoveries, notwithstanding an impressive catalogue of oil seeps and source rocks, the exception being the Eocene Talara Basin of Peru (1.2 billion barrels).

Large parts of South America are immature in exploration terms, and many basins of this continent show a great deal of potential for major discoveries to come.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995