Offshore Basins Characterization along the Northern and Central Andes: Impact on the Petroleum Systems Definition

Hermoza, Wilber¹; Rintjani, Emarty; Antich, Nuria; and Gutierrez, Manuel
¹[email protected]

The Pacific margin of the South American plate is occupied by offshore and onshore Tertiary basins, classically referred as forearc basins. Some of these basins are prolific hydrocarbon provinces in Latin America. The evolution of these basins was greatly controlled by oceanic plate subduction and related Andean uplift. Eastward subduction of the oceanic Plate beneath the continental South American Plate has been active for the last 200 Ma. It is well known that the subducting Pacific Plate is irregular and made up by several ridges and fracture zones that separate blocks with different rate, angle and direction. This resulted in different deformation styles on the overriding plate which controlled the tectono-stratigraphic evolution and the petroleum system development. The most striking tectonic changes occur in the transition between the Northern and Central Andes (Peru and Ecuador). Around 4 BBOE of RR have been discovered in this zone (i.e. Talara, Tumbes, Sechura and Progreso). HC accumulations in this area are mostly related to Tertiary and probably Cretaceous source rocks. Over 75% of the total RR are in Paleocene Talara Basin. The Neogene Tumbes Basin contains around 9% of the total reserves. The main source rock and reservoir in this basin is Miocene. The Progreso Basin located offshore SSW Ecuador holds around 7.5% of the total reserves. In this case, the main source rocks and reservoirs are Paleocene and Neogene.

Offshore regional cross-sections through this margin show that basins associated to Northern Andes are controlled by large strike-slip deformation, which generates narrow and deep highly confined Tertiary basins. Basin fill is characterized by huge sedimentary thickness of marine and coastal series which contain prolific and proved petroleum systems. Further south along the Central Andes (Southern and Central Peru) all the Tertiary offshore basins are larger in size but shallower in depth. Tertiary source rocks are probably present but they may not be mature everywhere due to the sedimentary thickness. The Pre-Tertiary section has been tentatively interpreted in some areas, including the hypothetic source rock intervals. Onshore, Mesozoic and Paleozoic outcrops contains fairly to good potential source rocks.

The tectonic and structural differences between the basins associated to the Northern and Central Andes must be taken into account for exploration evaluations as it has a huge impact in the associated petroleum systems present

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013