Offshore Guajira: An Underexplored Carbonatic Province at North of South America

Molinares, Carlos E.¹; Ramirez, Victor ¹; Gomez, Pedro ²; Pecuch, Daniel ²; Fiume, Giuseppe ²; Ghosh, Santosh ²; Audemard, Felipe ²
(1)Exploration, Ecopetrol, Bogota, Colombia. (2) DCS, Schlumberger, Bogota, Colombia.

The northern margin of South America contains one of the world’s densest concentrations of giant oil and gas fields. Surprisingly, the offshore area of this rich hydrocarbon region does not reflect the immense reserves of the onshore basins. However, there are considerable shallow water discoveries that reveal underexploration of the offshore areas. There are 7 Tcf of recoverable reserves in west of the Colombian Guajira peninsula (Chuchupa, Ballena and Riohacha fields), and upgraded 14 Tcf reserves in a new Paleogene carbonate play, in the northwestern Venezuela (La Perla Discovery).

Understanding the interactions between Caribbean Plate (CP) and South America Plate (SAP) is vital in understanding the petroleum systems, plays and prospectivity. The Guajira Offshore (GO) basins provide an excellent location for testing some assumption derived from current Caribbean tectonic models. Our recent studies, based on integration and interpretation of seismic lines and well data, evidenced two marked differences with previous tectonic models: First, absence of typical subduction features. Our 2D seismic interpretation led us to identify an important area with potential development of isolated carbonate buildups, overlaid by a Neogene sedimentary progradational system, with rare and small unconformities. The absence of compressional features in the GO basins implies that the deformation would be concentrated in a narrow and strongly deformed margin called South Caribbean Deformed Belt (SCDB). Second, absence of a Neogene typical “Island Arc”. Various Caribbean tectonic models seem to require large amounts of oceanic crust subducted during the Neogene. Nevertheless, there is no known Late Tertiary volcanic activity on the Guajira peninsula. On lines crossing the SCDB, underthrusting of the oceanic crust below the northwest margin of SAP has been interpreted. However, this regional feature has been called a “deformed zone”, due to the lack of volcanic and earthquakes defining a classical Benioff zone.

Recent basin modeling indicates that the Eocene-Oligocene, lower Miocene and lower part of the middle Miocene sections have potential for generation of thermogenic hydrocarbons. The GO exploratory potential is increased with the speculative presence of Cretaceous source rock in offshore areas. Indirect evidences of relicts of this cretaceous passive margin sequence have been recorded in recent studies by ECOPETROL S.A.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.