“Thin-Skinned” and “Thick-Skinned” Structural Control on the Evolution of a Foreland Basin Petroleum System – Cabuyarito and Medina Anticlines, Eastern Cordillera Llanos Foothills, Colombia

Abstract

The Cabuyarito anticline is located in the Llanos foothills on the eastern flank of the Eastern Cordillera of Colombia. To the northwest of the Cabuyarito anticline area is the Medina 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 to the northeast along strike is the giant Cusiana oil field. In the Cusiana field, light oil, gas, and condensate are found in a hanging-wall trap formed during the Miocene-Holocene deformation of the Eastern Cordillera. This study was based on a rich dataset provided by Frontera Energy Colombia, including a 3D seismic volume (357 km2, 5000 msec), 77 2D seismic lines (176 km), 18 wells with caliper, gamma-ray, sonic, density logs, checkshot surveys, and reports. We have produced new 3D horizon maps, seismic and stratigraphic interpretations, and 1D basin models. We have identified a number of promising stratigraphic plays in the relatively undeformed footwall block. A small fault-bend fold in the footwall of the Cabuyarito thrust appears to have 4-way closure for a Mirador Fm trap. 1D models suggest hydrocarbon generation from 5 to 8 Ma, similar to the Cusiana system, but high-angle normal and transpressive faults may have permitted hydrocarbon escape.

Just to the northwest, the Medina anticline is a fault-bend fold formed by Andean age (3-6 Ma) shortening. However, a “thin-skinned” bedding plane fault preceded the Medina anticline ramping to the surface along the Guaicaramo fault. The thin-skinned thrusting likely preceded the Early Miocene (18-22 Ma) Servita basement fault-propagation fold to the west. Our 1D basin model for the Medina well suggests that the Gachetá Fm source rocks began to expel oil from 12 to 6 Ma, before trap formation. Thus, some hydrocarbons may have escaped to the surface along the Guaicaramo ramp prior to Medina trap formation. The timing of thick-skinned and thin-skinned deformation, and trap formation were critical factors in the evolution of the Medina, Cabuyarito, and Cusiana petroleum systems.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018