Abstract: The Petroleum Geology of the Peruvian Sub-Andean Basins

Jeremy M. P. Mathalone, Manuel Montoya

There are three major basins in Sub-Andean Peru, the Maranon, Ucayali, and Madre de Dios basins. Together these cover over 370,000 sq km. These features extend considerable distances into Ecuador and Colombia to the north and Bolivia to the southeast.

Over five billion recoverable barrels of oil have been discovered to date in these basins, of which 1,350 million barrels are in Peru, together with almost nine trillion cubic feet of gas.

The Tertiary basins are the foreland troughs of the rising Eastern Cordillera of the Andes and are filled with up to four kilometres of Tertiary molasse clastics. These troughs of mainly Miocene age overlie extensive remnants of larger Paleozoic and Mesozoic basins. Three major compressional episodes can be recognized in the region. A Mid-Triassic event, an Early Cretaceous event which caused major unconformities in some areas, and a

regionally pervasive late Miocene (Quechua III) event which caused major thrusting and compressional folding over the majority of Sub-Andean Peru.

Oil and gas source rocks are recognized in Devonian, Carboniferous, Permian, Triassic, Jurassic and Cretaceous shales and shaley carbonates. Two main families of oils are differentiated in the Maranon basin, related to Cretaceous and Permian source rocks respectively. Three groups of hydrocarbon liquids in the Ucayali basin derive from Triassic, Permian, Carboniferous and Devonian sources. Oil samples in the Madre de Dios basin correlate to Devonian and Carboniferous shales.

A variety of trap types have been identified and seismic examples will be presented. The foreland can be divided into areas where pre-existing faults have been reversed by Upper Tertiary compression, and areas where this has not happened and older drapes etc. form traps. To the west, the thrusted Sub-Andean belt comprises areas where basement involved thrusts predominate and others characterized by detached thrusting. Within the Oriente/Maranon/Ucayali basin complex, there is at least one giant field in each trap type.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994