Subsurface mapping and 3D flexural modeling of the Putumayo foreland basin, Colombia

The Putumayo foreland basin (PFB) is located in southernmost Colombia and forms a 250-Kmlong segment of the 7000-Km-long corridor of Late Cretaceous-Cenozoic foreland basins formed by the eastward thrusting of the Andean mountain chain over Precambrian rocks. The current daily production of the Putumayo basin is ~90K BOPD of 15-35° API oil and 300K BOPD of 20-35º API oil in the contiguous Maranon foreland basin to the south, in Ecuador. This study uses ~4000 Km of 2D seismic data tied to 28 exploratory wells to describe the structure and stratigraphy of the basin. The PFB is located adjacent to the NNE-trending Colombian Andes that have been influenced by the oblique and shallow subduction of the Carnegie Ridge starting 8 Ma. 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, three main across-strike, structural zones, and five tectonosequences of the PFB are described based on seismic interpretations. The structural zones of the PFB include: 1) the 20-Km-wide, Eastern structural zone closest to the Andean mountain front characterized by inversion of older, Jurassic half-grabens during the late Miocene; 2) the 45-Km-wide, Central structural zone characterized by moderately-inverted Jurassic half-grabens; and 3) the 120-Km-wide, Eastern zone characterized by the 90-Km-wide, N-S trending Caquetá arch with a few slightly inverted normal faults at its crest. The five, mainly clastic tectonosequences of the PFB include: 1) pre-foreland basin Early Cretaceous sedimentary rocks; 2) the Late Cretaceous-Paleocene foreland basin deposits; 3) the Eocene foreland basin deposits related to the early uplift of the Eastern Cordillera; 4) underfilled foreland basin deposits of the Oligocene-Miocene age; 5) overfilled foreland basin of the Plio-Pleistocene age. I used 3D flexural modeling to identify the present-day tectonic elastic thickness (Te) values for the lithosphere below PFB, in order to model the location of the sedimentary-related and tectonically-related forebulges in PFB units from the Cretaceous to Oligocene. This analysisshows two pulses of rapid, foreland-related subsidence during the Late Cretaceous-early Paleocene and the Oligocene-Miocene. Despite present-day oblique thrusting of the mountain front, the PFB basement flexure reveals a tectonic forebulge located in the Eastern structural zone that acts as the updip limit for most hydrocarbons found in the basin.