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Abstract: Petroleum Systems Along the Foldbelt Associated to the Maranon-Oriente-Putomayo Foreland Basins

Robert Marksteiner, Antenor M. Aleman

Along strike variations in structural style of the foldbeft associated to the Maranon-Oriente-Putumayo (MOP) Basins and timing of deformation accounts for the major variations in their petroleum systems. Space-time changes in structural style controlled the timing of maturation and generation as well as reservoir and seal quality. Source rock distribution and richness could vary along the foldbelt, however, they are difficult to document.

The Foldbelt associated to the Oriente and Putumayo Basins is characterized by thick-skinned style of deformation and contains the only commercial accumulations. A thick sedimentary wedge of the Tena Formation in front of the Napo and Cutucu Uplifts documents Late Cretaceous/Paleocene deformation (Peruvian Phase). AFT data in the Putumayo, Napo and Cutucu Uplifts documents a Middle Eocene Uplift (Incaic Phase) followed by a Late Miocene Pliocene renewal of uplift. The main phase for hydrocarbon generation and migration was from Late Cretaceous to Middle Eocene, therefore, the productive structures must have an older component. Biodegradation and water washing accounts for the destruction of the largest accumulation of heavy oil in the southern plunge of the Napo Uplift.

The Peruvian segment includes the salt-related Santiago and Huallaga Foldbelts which are still poorly explored. Although there are strong indications for salt movement and basin inversion since Mesozoic times, the main episode of folding and thrusting was Late Miocene to Pliocene. This is supported by AFT and modern seismic data. Although there are several structures showing Mesozoic thinning against the salt, the major episodes of salt withdrawal took place during the Tertiary. This accounts for significant burial of the reservoir rocks with concomitant reduction of the primary porosity.

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