--> ABSTRACT: Macro Seepage in the Puna Basin, Argentina: Inferences as to Source Quality, Type, and Maturity, by Vaughn D. Robison; #91020 (1995).

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Macro Seepage in the Puna Basin, Argentina: Inferences as to Source Quality, Type, and Maturity

Vaughn D. Robison

As part of an evaluation of the La Puna area of Argentina, macro seeps and potential source rocks were sampled in the outcrop during the initial phase of exploration. The data generated from these samples provided evidence of the stratigraphic and geographic location of mature source rocks and possible migration routes prior to drilling.

All of the seeps exhibit varying degrees of biodegradation complicating oil-oil correlations, however, geochemical characterization suggests that all have a common source. Several potential source rocks were sampled and the Cretaceous Yacoraite Formation was identified as an organic-rich source that contains oil-prone facies. Characterization of the source horizons within the Yacoraite indicate the presence of two distinct organic facies. Even though distinct facies exist, differences between the two are minor and both facies contain oil-prone organic matter.

Oil to source correlations suggest that the Barro Negro facies of the Yacoraite is the primary source for the macro seeps in the basin. The establishment of a correlation provided evidence that at depth, the Barro Negro facies was present and had generated and expelled hydrocarbons. Surface hydrocarbon occurrences could not be attributed to the Arroyo Vicunayoc facies of the Yacoraite.

Subsequent drilling of the Cerro Ramada X-1 well discovered sub-commercial quantities of hydrocarbons. After accounting for differences due to biodegradation of the seeps, the hydrocarbons in the Cerro Ramada well could be correlated back to the seeps as having a common source. However, minor differences between the seeps and Cerro Ramada hydrocarbons indicated that the Barro Negro facies of the Yacoraite did not source the Cerro Ramada oil. Rather, the Arroyo Vicunayoc facies of the Yacoraite correlates most closely with the Cerro Ramada oil indicating a complex source facies and migration history in the basin.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995