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Tectonic Evolution of the Southern Llanos Basin, Colombia and its Significance for Hydrocarbon Prospectivity

Moreno, Catalina1 and Escalona, Alejandro
1[email protected]

The Llanos foreland basin is the latest stage of a complex Paleozoic-Recent multiphase evolution of eastern Colombia. A basin evolution is presented based on ~5000 km of 2D seismic data and 12 exploratory well observations in the southern part of the basin from Paleozoic to present. Recent hydrocarbon discoveries in the gently dipping Cenozoic rocks in the eastern part of the foreland basin reveal a positive relationship betweenbasement structures, that can be clearly identify in gravity maps, and the hydrocarbon potential. These structures are poorly understood in their origin and reactivation, in comparison to the better explored traps in the fold and thrust belt of the Eastern Cordillera foothills and the flexural normal faults in the foredeep area.

Four main tectono-sequences were identified: 1) A fold and thrust belt of Neoproterozoic rocks with presence of triangular zones formed during a compressional event in the Lower Paleozoic; 2) The Upper Paleozoic graptolitic shales deposited in piggy back basins and the Paleozoic foredeep; this sequence has potential source rocks; 3) The Upper Cretaceous- Paleocene sequence consists of shallow marine sediments deposited in the distal area of the Cretaceous foreland basin of the paleo- Central Cordillera; and 4) The Oligocene- Pliocene sequence dominated by fluvial and deltaic sedimentary rocks, which are related with the uplift of the Eastern Cordillera.

As a result of this multiphase evolution, several types of traps were developed, which include: Cenozoic thrusts anticlines related with the uplift of the Eastern Cordillera; normal faults on the foredeep hinge areas; Cretaceous stratigraphic traps; and piggy back basins formed by the reactivation of the Lower Paleozoic fold and thrust belt.

The hydrocarbon exploration risk is related with the positive relief of the Paleozoic fold and thrust belt until the Oligocene. This Paleo-high represented a paleo-barrier for hydrocarbon migration from the Cretaceous source rocks from the Eastern Cordillera to the forebulge in the east. However a Local Paleozoic kitchen is proposed along the Paleozoic piggy back basins and the Paleozoic foredeep.

 

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013