David A. Wavrek¹, Daniel D. Schelling², Mariano L. Vela³, Jorge J. Hechem⁴, Kevin R. Allison⁵

(1) Petroleum Systems International, Inc, Salt Lake City, UT
(2) Structural Geology International, Salt Lake City, UT
(3) Chevron Overseas Petroleum Inc, San Ramon, CA
(4) Repsol-YPF, Heuquen, Argentina
(5) Pangaea Energy LLC, Highlands Ranch, CO

ABSTRACT: Petroleum Systems of the San Jorge basin, Argentina

The San Jorge basin is located in the center of Patagonia and contains three distinctive structural zones: the West flank (Rio Mayo embayment), the San Bernardo foldbelt, and the East flank (Sag basin) with offshore extension. The primary petroleum systems are designated: D-129 - Bajo Barreal (!)in the East flank and foldbelt, whereas it is the Aguada Bandera - Bajo Barreal (!) in the west. On the southern margin of the West flank is a region of oil fields that have a hydrocarbon charge of mixed origin (D-129 + Aguada Bandera). The petroleum systems charged by the D-129 are dominant in volumetric terms, and this source rock formed in an extensional lacustrine setting that contained a hypersaline to brackish anoxic water column. The Aguada Bandera source rock also formed in an extensional lacustrine setting, but with a freshwater column and evidence for a marine incursion at the top of the depositional sequence. Systematic variation in water column chemistry are linked to source rock quality as a function of high- and low-stands in the lake level. Specific topics to be addressed within this petroleum systems sythesis include: the variation in oil quality, the potential for oil vs. gas prospects in the basin center and offshore, an explanation for barren structural traps in the foldbelt, and the potential for re-migrated hydrocarbons in different parts of the basin. It is concluded that the most significant aspect to understanding the petroleum systems of the San Jorge basin is the relationship between timing of hydrocarbon generation in context of effective seal formation.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado