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The Geodynamic Evolution of the Sinu Offshore Basin and its Importance in Determining the Prospectivity of the Magdalena Fan, Offshore Colombia

Abstract

The Magdalena Fan, offshore Colombia is often thought of as a prospective frontier area for hydrocarbon exploration. However, the Sinu Basin, into which the Magdalena Fan drains, has experienced a complex series of accretionary events, wrench faulting and under thrusting associated with the insertion of the Caribbean Plate. As such uncertainty persists concerning the presence, quality and areal extent of major petroleum system elements. This presentation aims to address some of this uncertainty by considering the geodynamic evolution of the region using a global, palinspastic geodynamic model. Source rock presence is deemed to be low risk due to the occurrence of oil seeps from the adjacent onshore Sinu-San Jacinto Fold Belt and hydrocarbon shows in both the on and offshore part of the basin. However, it should be noted that most of the wells drilled in and around the Magdalena Fan have been dry. The predicted age of the accreted basement complexes would seem to preclude the presence of a Late Cretaceous La Luna-equivalent source rock. However, it is possible that slithers of Late Cretaceous organic-rich material have been incorporated into the accretionary complexes. A more likely source rock is the Tertiary, gas-prone Cienaga de Oro Formation, although the presence of a Maastrichtian Cansona Formation equivalent should not be ruled out. Reservoir presence is also likely to be low risk, although important hinterland uplift events associated with terrane collision along the western margin of South America will result in a shift in the provenance of derived clastics. Uplift of the various Colombian Cordilleras that bound the Magdalena Valley basins manifests itself in shifting populations of detrital zircon U-Pb dates (Nie et al. 2010) that has implications for the reservoir quality preserved down systems tract. Seal is likely to be high risk due to overpressure (Amaral et al. 2003) that results from rapid late burial as a direct result of hinterland uplift events. In this presentation we aim to illustrate how a robust geodynamic framework constrained by a radiometric dataset derived from the public domain can be employed to draw some preliminary conclusions on the likely hydrocarbon prospectivity of a frontier basin.