Abstract: Exploration for Stratigraphic Traps in a Foreland Basin Using a Sequence Stratigraphic Simulation: Examples from the Eocene/Oligocene of the Apure-Llanos Basin, Venezuela

John Reistroffer, Phillip A. Levine, Christopher G. St. C Kendall, Anahy Finno

Foreland basin depositional sequences provide a sensitive record of the interaction between tectonism, eustatic sea level fluctuations, and sedimentation rates. Interplay between these controlling factors creates sedimentary geometries which are unique to this tectonic setting and form excellent stratigraphic hydrocarbon traps. Incised valley fill deposits, forced regression deposits, and combination structure-stratigraphic traps are the predominant reservoir types. In an effort to extend our understanding of the development of these traps, the sequence stratigraphy of a regional seismic transect through the Apure-Llanos basin was simulated.

From the Late Eocene through Oligocene, the Apure-Llanos basin was characterized by multiple phases of compression and a southeast migrating depocenter. Sands of the Mirador and Carbonera formations, which onlap the Arauca Arch to the southeast, were shed from the Guyana craton and were cannibalized from sediments along the deformation front to the northwest. These sands comprise the principal reservoirs in the study area. Shales of the Leon Formation, which act as a regional seal, were deposited during rapid flexural subsidence and eustatic sea level rise during the early Oligocene. The Arauca Arch acted as a focal mechanism for east and southeast migrating hydrocarbons.

Simulation results predict an important stratigraphic pinch out of the Mirador Formation sands against the Arauca Arch, which correlates with the Arauca Field in Colombia to the southwest. Also, modeling indicates that minimal Tertiary oil production in the La Victoria Field to the east is due to the lack of an adequate seal. Our results provide a conceptual model which predicts hydrocarbon reservoir and seal relationships in a foreland basin setting with limited data control.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela