Llanos Basin

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The Llanos Basin is one of the most prolific and largest sedimentary basin in Colombia. Located along the western margin of the Guyana Shield it covers more than 200.000 km², bounded westward by the Andean Cordillera.[1] These foothills and foreland basin are enclosed in the north by the Columbia-Venezuela Border. Fig. 1 outlines the reagion of the basin. The Departments of Columbia within the Llanos basin include Arauca, Casanare, Meta, portions of eastern Boyaca and Cundinamarca, and southernmost Norte de Santander.

Fig. 1 Regional map of the Llanos Basin, eastern Colombia


Fig. 2 Locations of major oilfields

The Llanos foreland basin of Colombia is the country's most prolific oil producer, with the most known oilfields found in normal fault traps created during flexure of the foreland basin. [2] The Llanos Basin has cumulative production of about 10 MM (million) barrels oil-equivalent and contains some of the biggest oil fields in Colombia such as Caño Limon, Cusiana and Cupiagua. Around four and three billion barrels oil-equivalent of recoverable reserves have been discovered in the foothills and foreland sectors of the basin, respectively. [3] The exploration activity started in the 1940’s, but it was only in the 1970’s and 1980’s that the most important fields were discovered. This basin can be divided by its two distinctive structural domains: the foothills to the west and the foreland to the east. With a production of approximately 690,000 BOPD, the LBC represents about 70% of the Colombian national production of crude oil and is the focus of high expectations in exploration, especially for heavy oil.[4]

Llanos Foothills

The western area is characterized by a compressive and transgressive deformation belt and hosts giant Colombian hydrocarbon fields such as Cusiana, Cupiagua, Volcanera, Capachos, and Gibraltar as seen from Fig. 2.

Llanos Foreland Basin

Sometimes referred to as Eastern Llanos the landscape is less deformed than the foothills and is characterized by a Neogene basin-fill affected by normal faults and gravitational features. Notable discoveries include:Caño Limón, Caño Yarumal and Rubiales.


These risks include, but are not limited to, inflation or lack of availability of goods and services, environmental risks, drilling, the uncertainties involved in interpreting drilling results and other geological data, completion and production risks, equipment failure, availability of labor, unexpected geological or other effects, uncertainties relating to fluctuating oil and gas prices, regulatory changes and availability of capital. [5]

Geologic Structure

Fig. 3 Geological Structure

The Llanos foreland basin of northeastern Colombia is an elongate and asymmetrical sub-Andean foreland basin formed during Late Cretaceous to Recent convergent events between the Andean Mountains and cratonic rocks of northwestern South America.[2] Basin development began during the Triassic to the earliest Cretaceous with a synrift megasequence related to the separation of North and South America in the proto-Caribbean.[2]

The most import extensional event occurred east of the Andean subduction zone, in the current Eastern Cordillera and Magdalena Basin, during Early Cretaceous times. This back-arc mega-sequence was dominated by shallow-marine sedimentation and produced excellent source rock (Gacheta). The accretion of the Western Cordillera stopped the marine deposition during early Maastrichtian.[1] The Late Eocene-Early Miocene Carbonera Formation has been described as a thick succession of interbedded, sand-rich members and muddy members deposited on fluvial plains with local tidal-influence as depicted in Fig. 3. This dominantly sinuous fluvial system becomes increasingly sandier towards the flanks of the basin. [2]

Petroleum System

Source Rock

The Llanos Basin is a prolific petroleum province where there are different source rocks intervals, and also numerous reservoirs. The marine calcareous intervals of the Fomeque Formation and the marine shales of Gacheta Formation, are considered as the main source rocks of the basin. [6] Inside the northern oils, two sub-families can be identified. The Foothills oils, like Capachos could have been charged from Tertiary source rock or different organic facies of the same Cretaceous source but with higher terrestrial input than the oils from the North Llanos foreland basin. According to the plot, the oils found in the southern area apparently reached a lower maturity level than the rest of the oils.[1]


Fig. 4 Schematic east-west cross section showing petroleum system elements in the Llanos Basin

The most important reservoir interval in the Llanos Basin consists of Upper Eocene sandstones in the Mirador Formation, but Fig .4 shows oil accumulations have also been encountered in Upper Cretaceous sandstones (Une, Gachetá and Guadalupe Formations), in the Paleocene Barco Formation, and in the Oligocene Carbonera C7 interval.[3]

Trap and Seal

Traps consist of east-dipping normal faults caused by uplift during the Oligocene and Early Miocene along the eastern bank of the Andes, and by later orogenic loading. As shown in Fig. 3, shale seals occur throughout the Cretaceous-Tertiary succession and include the Carbonera C8 interval, the overlying Leon Shale, the Los Cuervos Formation and the upper part of the Guadalupe Formation.[3]


There have been two migration pulses. The first one occurred during the Upper Eocene-Oligocene. The second began in Miocene times and continues at present.[7] Hypothetical Lower Cretaceous source rock could have expelled hydrocarbons since Late Cretaceous, but the migration may have been essentially westward, toward the Magdalena Valley.[1]

Petroleum Potential

Toward the Miocene, oil accumulations occurred in shallow reservoirs in the eastern and southwestern parts of the LBC, where the temperatures were less than 70°C. Under these conditions, biodegradation processes can take place, resulting in heavy oil reserves.[3] Tertiary source rocks like Los Cuervos and Carbonera are also mature at present day along the Eastern Cordillera, but expelled quantities could be much lower in comparison with Gacheta.[1] This basin has been moderately drilled and subtle stratigraphic traps have not been deeply studied. The southern and eastern portions of the basin are potential areas for hydrocarbon accumulation, where meteoric water forming hydrodynamic traps affects pinch-outs of reservoirs. The south-western part, south of the Castilla Field, is also a highly prospective area. [7]

Engineering Aspects

Fig. 5 Pikovsky & Guberman prognostic map

In 1986 the model proposed by Professor Yury Pikovsky and Professor Shelia Guberman(Moscow State University) assumes that petroleum moves from the mantle to the surface through permeable channels created at the intersection of deep faults. The technology uses 1) maps of morphostructural zoning, which outlines the morphostructural nodes (intersections of faults), and 2) pattern recognition program that identify nodes containing giant oil/gas fields. It was forecast that eleven nodes, which had not been developed at that time, contain giant oil or gas fields. These 11 sites covered only 8% of the total area of all the Andes basins.[8]

Since publication of the prognostic map in 1986 four of the six giant oil/gas fields were discovered in the Llanos Basin: Cano- Limon, Cusiana, Capiagua, and Volcanera. All discoveries were made in places shown on the 1986 prognostic map as promising areas. The result is convincingly positive, and this is a strong contribution in support of abiogenic theory of oil origin. The red dots in Fig. 5 indicate highly promising knots where giant oil/gas fields were discovered after 1986. [8]

Further Reading

Regional Study and Petroleum System Modeling of the Eastern Llanos Basin

Origins of formation waters in the Llanos foreland basin of Colombia: geochemical variation and fluid flow history

Evaluation of Crude Oils From the Caracara and Tiple Areas, Eastern Llanos Basin, Colombia: Palaeo Biodegradation and Oil Mixing


  1. 1.0 1.1 1.2 1.3 1.4 Vayssaire, A., Abdallah, H., Hermoza, W., & Figari Negri, E. G. (2014, January 13). Regional Study and Petroleum System Modeling of the Eastern Llanos Basin*. AAPG Datapages. http://www.searchanddiscovery.com/pdfz/documents/2014/10564vayssaire/ndx_vayssaire.pdf.html.
  2. 2.0 2.1 2.2 2.3 Torradoa, L., CarlosCarvajal-Arenas, L., Mann, P., & Bhattacharya, J. (2020, April 20). Integrated seismic and well-log analysis for the exploration of stratigraphic traps in the Carbonera Formation, Llanos foreland basin of Colombia. Journal of South American Earth Sciences. https://reader.elsevier.com/reader/sd/pii/S0895981120301206?token=FA077E7B9C182C63D6D0C872DACE1C9C7B8FDD5FE67EE76946465A9C9E90F4ABD3689D26314EE96DD4FF02FF1B4F1390&originRegion=us-east-1&originCreation=20210418233026.
  4. Gonzalez‐Penagos, F., Moretti, I., France‐Lanord, C., & Guichet, X. (2014, June 30). Origins of formation waters in the Llanos foreland basin of Colombia: geochemical variation and fluid flow history. Wiley Online Library.https://onlinelibrary.wiley.com/doi/full/10.1111/gfl.12086.
  5. ThreeD Capital Inc. (2013, February 25). Brownstone Energy Spuds Calacho #1 Well, Llanos Basin, Colombia. GlobeNewswire News Room. https://www.globenewswire.com/en/news-release/2013/02/25/1365381/0/en/Brownstone-Energy-Spuds-Calacho-1-Well-Llanos-Basin-Colombia.html.
  6. Velandia, M. (2009, September). Petroleum System Variations In The Llanos Basin (Colombia). ResearchGate. https://www.researchgate.net/publication/327510466_Petroleum_System_Variations_In_The_Llanos_Basin_Colombia.
  7. 7.0 7.1 Petrotech , E. L. (2012, December 31). EVALUATION OF THE INTERESTS OF HEAVY EARTH RESOURCES, INC.’s 2012 YEAR-END RESERVE EVALUATION IN THE MORICHITO BLOCK IN THE EASTERN LLANOS BASIN, COLOMBIA. SEC.gov. https://www.sec.gov/Archives/edgar/data/1301874/000146929913000112/hevi991.htm.
  8. 8.0 8.1 Guberman, S., & Pikovskiy, Y. (2018, September 15). The field test confirms the prognosis of the location of giant oil and gas fields in the Andes of South America made in 1986. Journal of Petroleum Exploration and Production. https://link.springer.com/article/10.1007/s13202-018-0553-1.