Geologic Constraints and Controls on Petroleum Migration in Eastern Venezuela Basin

R. Aymard, D. R. Baker, R. Lander

This work focuses on the petroleum accumulations of the Anaco, Greater Oficina, and Faja (heavy-oil) areas along a north-south transect through the Eastern Venezuela basin. We believe these major accumulations are directly related to the Tertiary generative basin defined by the enormous fill of Tertiary sediment extending from the Guayana shield shelf edge on the south to the loci of Tertiary depocenters adjacent to the Venezuela coastal cordillera on the north. Factors that place constraints on the evolution of petroleum development in the Eastern Venezuela basin include: (1) accumulations of heavy oil in the Faja are unusually large; (2) petroleum in the Greater Oficina area is dominantly paraffinic-napththenic, but is variable; (3) paraffinic (waxy) petroleum occurs wi hin the Anaco area; (4) petroleum is concentrated in the basal part of the Tertiary section; (5) most of the petroleum in sandstone reservoirs occurs near the shelf edge within immature sections, i.e., below the oil-generation threshold; and (6) petroleum is trapped on the north (basinal) side of faults. The major controls of petroleum variability and occurrence appear to be: (1) the temporal relationship between the generation and fluid expulsion history of the Tertiary basin fill; (2) the stratigraphic framework involving distinctive regressive-transgressive sequences that progressively onlap the shelf edge and are characterized by repetitive sedimentary packages (lower prodelta and upper transgressive shales separated by medial sandstones), which behaved as semi-independent units of g neration, expulsion, and migration; (3) the related temporal development of the faults as effective seals.

AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.