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Structural Evolution and Petroleum Potential of Putumayo Foreland Basin, Colombia, From Subsurface Mapping and 3-D Flexural Modeling

Pachon, Luis F.; Mann, Paul; Cardozo, Nestor

The Putumayo foreland basin (PFB) covers 28,000 km2 of southernmost Colombia and forms a 250-km-long segment of the 7000-km-long corridor of late Cretaceous-Tertiary foreland basins formed by the eastward thrusting of the Andean mountain chain over Precambrian cratons of South America. The current daily production of the Putumayo basin is ~90K bopd barrels of 15-35 API oil and 300K bopd of 20-35 API oil in the contiguous foreland basin to the south in Ecuador. This study uses ~4000 km of 2-D seismic data tied to 17 exploratory wells to describe the structure and stratigraphy of the PFB. The wedge-shaped basin stratigraphy is used to model the lithospheric flexural deflection. PFB resides adjacent to the Andes adjacent to the active Pacific subduction margin of South America and has been subject to collision and shallow subduction events. Based on mapping of the subsurface of the PFB and comparison with published works from the southward continuation of the PFB into Peru and Ecuador, we propose three main across-strike, structural provinces for the PFB: 1) the 20-km-wide, eastern Orito zone is characterized by inverted half-grabens with structural relief produced during the Late Miocene; the best expressed, inverted rift is the Orito mountain front structure that exhibits more than 300 m of reverse fault throw of Tortonian age; 2) the 45-km-wide, central zone is characterized by inverted normal faults of the same age as the western area but these faults exhibit only 20 m of reverse fault throw and are commonly of Paleocene age; and 3) the 120-km-wide, eastern zone is characterized by the 90-km-wide, N-S trending Caquetá arch with only a few slightly inverted normal faults at its crest; the basement of the Caquetá arch composed of deformed Paleozoic sedimentary rocks. We used 3-D flexural modeling to backstrip foreland basin units from Cretaceous to recent age; this analysis yields two pulses of rapid, foreland-related subsidence in the Eocene and Miocene. Despite present-day oblique thrusting at the mountain front, arching of the PFB basement using a standardized elastic thickness is pronounced and reveals a peripheral bulge that acts as the updip limit for most oil in the basin. Modeling predicts that the modern forebulge occupies the Caquetá arch and the zone of maximum flexure has been along the western area of the central zone since Oligocene. Profiles are used to illustrate possible traps in the basin that may have been overlooked.

 

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013