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Possible Petroleum Systems in Espino Graben, Venezuela Suggest New Exploration Frontier


Pestman, Pieter1, Masashi Hirano1, J. Michael Moldowan2 (1) Teikoku Oil Co. Ltd, Caracas, Venezuela (2) Stanford University, CA


The Espino Graben is one of the future exploration plays in Venezuela. It is situated in the Guarico Sub-basin, Eastern Venezuela, and formed when the Central Atlantic opened. It is filled with Mesozoic (probably mostly Jurassic) syn-rift sediments, which are overlying a Paleozoic pre-rift sequence.

Geochemical data (diamondoids) obtained from oils in Tertiary sediments indicate that, although most of the oil has been generated by Tertiary and Cretaceous (i.e. post-rift) source rocks, some oil comes from a highly mature source. Upper Jurassic and several Paleozoic intervals were identified as potential sources for this oil.

Further geochemical analyses and basin modeling were carried out in order to obtain more information about the possible petroleum system(s) in the Espino Graben. Geochemical analyses included an evaluation of diamondoid and biomarker isotopes in oil samples from the Espino Graben and some Jurassic/Paleozoic oil and source-rock samples from other areas. Basin modeling included a tectonostratigraphic and paleogeographic eval­uation of Eastern Venezuela; it yielded information about the timing of hydrocarbon genera­tion, possible migration pathways, and potential traps.

It was concluded that Jurassic, and possibly also Paleozoic, source rocks may have been generating hydrocarbons in the Espino Graben and that these may have been trapped in structures within the graben. However, uncertainty remains regarding (1) the presence of effective seals in the syn-rift tectonosequence, and (2) reservoir quality.