Thin-skinned and thick-skinned structural control on the evolution of a foreland basin petroleum system - Parrando and Guavio anticlines, Eastern Cordillera Llanos foothills, Colombia

Abstract

The Parrando anticline is located in the Llanos foothills on the eastern flank of the Eastern Cordillera of Colombia. To the northwest of the Parrando anticline area is the Guavio anticline, a large fault-bend fold, a structure that appears to be an unbreached trap with four-way closure and seal, but test wells show no commercial amounts of petroleum. Just 65 km to the northeast along strike is the giant Cusiana oil field. This study presents new 3D horizon maps, seismic and stratigraphic interpretations, and 1D basin models based on a 3D seismic volume (246 km2 5000 msec), 70 2D seismic lines (176 km), 18 wells with well log data and final well reports. A small fault-bend fold in the footwall of the Parrando thrust appears to have 4-way closure for a Mirador Formation trap. 1D models suggest hydrocarbon generation from 8 to 5 Ma, similar to the Cusiana system, but high-angle normal and transpressive faults may have permitted hydrocarbon escape. Just to the northwest across the Guaicaramo fault, the Guavio structure was formed by overlapping fault-bend folds (total relief 3.5 km) during late Miocene-Pliocene age (6-3 Ma) shortening (minimum 20 km) and inversion of the Guaicaramo normal fault. Unlike previous models, we interpret the basement fold as formed by a ramp from pre-Cretaceous basement to a double wedge fault, folding the Guaicaramo thrust footwall rocks. A thin-skinned bedding plane thrust fault ramping to the surface along the Guaicaramo fault may have preceded the formation of the Guavio anticline. Our 1D basin model for the Medina-1 well predicts that the Gacheta Formation source rocks began to expel oil at 18 Ma, at least 10 Myr before trap formation. The timing of thick-skinned and thin-skinned deformation, and trap formation were critical factors in the evolution of the Guavio, Parrando, and Cusiana petroleum systems. Most of the Guavio deformation results from repeated inversion of the Mesozoic Guaicaramo basin-bounding normal fault.