Evaluation of Potential Petroleum System in Jurassic Strata of the Espino Graben, Eastern Venezuelan Basin

N. C. Acosta¹, L. Duerto¹, A. Pico², P. Bastos¹, and R. Mendoza^1
1Exploration - Oriente, PDVSA, Puerto La Cruz, Venezuela
²BEICIP, Caracas, Venezuela

A new petroleum system in Jurassic sequences of the Espino Graben is postulated. Traditionally, the following source rocks were reported: the Cretaceous marine Querecual Formation and a more terrigenous Tertiary source, e.g. Roblecito and Carapita formations. Here we report hydrocarbon shows which, although similar to Cretaceous oils, share some characteristics with Jurassic oils in Peru and Argentina based on distributions of age-indicative biomarkers (e.g. 24-norcholestane and dinosteranes).

Petroleum systems were strongly affected by the tectonic history of the area. Six tectonic events, starting in Cambrian and ending in Miocene, have been interpreted. Their influence on the different elements of petroleum systems produced several risks in the accumulation and preservation of hydrocarbons.

The preliminary results indicate that the putative Jurassic interval in the southern, shallower part of Espino Graben is expelling oil now. However, in the center of the graben, where Jurassic source rocks reached their maximum depth, oil generation would have begun at 80 m.y. Unfortunately any hydrocarbons expelled in the central graben would have been lost because of intensive erosion caused by Late Cretaceous tectonic arch formation. At the present we are acquiring new data in order to validate the Jurassic petroliferous system and to contribute information on other possible prospective sequences (i.e. Palaeozoic).

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas