The Triassic-Jurassic Petroleum Systems in the Subandean Basins. Paleogeography and geochemistry of the organic rich sequences

URIEN, C.M., SCHIEFELBEIN, C. & ZAVATTIERI, A.M.

Cartagena, Colombia

Simposio; X Simposio Bolivariano Exploración Petrolera en Cuencas Subandinas (Cartagena), Colombia; 2009

The Cuyo basins are a continental landlocked intermountain rift system covering an area of about 40,000 sq km, situated on the west flank of the Pampean Ranges and Precordillera. The basins are a composite of several smaller rift features that formed during the Triassic as result of postorogenic relaxation and extension that continued into the early Jurassic. Oil seeps in Cacheuta region dates from the late XVlll Century. Commercial discovery reported from 1913, and Co. Cacheuta field since 1920‘s. Since 1930, Y.P.F. and after 1962 private companies, they operates this basin achieving a cumulative oil production in the order of 3,500 MM BBO and 256 TCF. At the southern end of the basin complex and farther removed from the Cordilleran front, the Alvear and Desaguadero depocenters were much less disturbed and only display the development of low-relief tanstensional structures. Waxy oils produced from Triassic and Tertiary strata constitute one of the oldest (since 1800`s) and most important petroleum resources in the Central Argentina`s Subandino. Oils are primarily derived from organic-rich shales of the Late Triassic Potrerillos - Cacheuta formations deposited in wholly freshwater fluvio / lacustrine and lacustrine environments. Significant hydrocarbon generation only occurred during the last 10 Ma. following a rapid subsidence episode of thick Tertiary overburden. This region is analyzed under multidisciplinary approach to further evaluate and predict the occurrence and distribution of petroleum systems active in this important area, as well as their association with other Sub Andean basins. Paleoentology data and oil and source rock geochemistry are integrated with a G&G (4G) and combined with recent thermal modeling results to understand facies and thermal variability across the basin resulting in a realistic evolutionary model. This paper describe also how a multivariate statistical comparison of oil data representing all major Subandean basins can be used to distinguish important Triassic and Jurassic source rocks such as those occurring in the Neuquen - Mendoza Basins of Argentina and the Titicaca – Ucayali - Marañon of Peru.