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New Stratigraphic Interpretation of the Depositional History from Upper Oligocene-Lower Miocene Eastern Venezuela Basin

Santiago, Nubia 1; Herrera, Meylin 1; Salomon, Marien 1
1 Exploration, PDVSA, Puerto La Cruz, Venezuela.

Existing interpretation of the Lower Miocene sedimentation in the eastern Venezuela Basin are in need of revision in order to make reliable correlations that allow us to predict the best position to find turbidites systems. Published facies maps indicate that the Lower Miocene of the area between the present deformation front and the folded belt is characterized by deep water sedimentation dominated by shale with thin layers of turbidites (Lower Miocene) onlap on the basal foredeep unconformity.

The stratigraphic interpretation is based on biostratigraphic data of 45 wells, studies of 5725 feet of conventional cores, and log analysis of all wells. The Upper Oligocene-Lower Miocene interval was divided in two distinct stratigraphic units that contain important petroleum reservoirs. The lowermost succession (Sequence S1-Upper Oligocene-Lower Miocene) from the eastern Venezuela Foreland Basin is characterized by different depositional system especially wave and river dominated deltas, which suggests an apparent process-regime change from west to east. The uppermost unit (Sequence S2-Lower Miocene) records a wave dominated deltas with development of delta front deposits to the south area and pro-delta-offshore deposits to the north area. Above this unit a very high transgressive system begins as a result of overall transgression in the basin through time.

The new interpretation of the Upper Oligocene - Lower Miocene sedimentation suggests a delta complex development with a shelf break located farther north of the present deformation front. The fluvial deltaic sedimentation stored sand budget on the shelf, with correspondingly large volume available for the deepwater areas. Therefore, prominent sand bypass for the shelf into deepwater could be deposited northwards through Santa Barbara, Mulata and El Furrial area.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009