Maracaibo Basin

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The Maracaibo basin is located mainly in the northwestern area of Venezuela with the southern tip slightly entering Colombia. This basin lies between the Andes de Merida and Sierra de Perija. It is approximately 23,572 square miles, of which 5000 square miles sit under Lake Maracaibo. [1] While the Maracaibo basin has been known for centuries, it wasn't until 1914 that The Shell Company began to show interest in exploring the area. It was 1917 when drilled its first well in the Bolivar Coast field, thus discovering its production capabilities. After the success of the discovery well interest was sparked in other companies, drawing them out to begin their own exploration of the area. [1]

Figure 1 Outline of the Maracaibo Basin and where it lies in Venezuela and Columbia (Wikimedia Commons, the free media repository, 2021)

History of The Basin

Tectonic History

The Maracaibo basin has undergone many evolutionary stages dating back to the Jurassic period. The three main stages occurred in the Jurassic, Cretaceous and Paleo-Eocene eras.[2] In the Jurassic period, when Pangea was breaking up rifting led to the separation of the north and south American plates. At this time, the Caribbean plate also began to migrate eastward. During the Cretaceous period, the South American plate developed into a passive margin following rifting and the creation of oceanic crust between north and south Americas.[3] From the eastward migrating Caribbean plate, it eventually collided with the South American plate in the Paleo-Eocene period. This collision turned the passive margin of the south American plate into an active margin and the Caribbean plate began to subduct beneath the South American plate. This greatly affected the northwestern region of South American and left large amounts of deposits.

Depositional History

In the Maracaibo basin we see deposits of igneous and metamorphic rock of the Perija range from the pre-Cambrian. The Cretaceous is mainly seen in the rocks along the margin of the basin. These rocks were mainly sandstones and conglomerates of the Rio Negro formation.[1] During the early Miocene, the uplift of the mountain ranges surrounding the Maracaibo basin controlled the disposition of shallow-marine, costal and nonmarine sedimentary rocks in this area. These sedimentary deposits have created the most important shale top seals for the basin and the Bolivar Costal Field. [4]

Petroleum Elements

Source Rock and Migration

The Maracaibo basin contains organ-rich marine deposited Cretaceous shales in the La Luna formation that are the principal source rocks. [5] The migration in this basin occurs along the major fault systems.[6] The biggest risk seen in this formation is the retention of gas in the La Luna formation source rock. Additionally it is possible that this gas has migrated into the tight sandstones, however, it is uncertain whether or not these tight sandstones exist. [7]

Figure 2 Prospective areas of oil and gas production in the Maracaibo Basin (Advanced Resources International, Inc., 2013)

Reservoir Rock

The main reservoir rocks in the Maracaibo Basin are fluvial-deltaic sandstones of the Eocene Misoa Formation and deltaic sandstones of the Miocene Lagunillas Formation.[6] The Miocene Lagunillas formation has been the most prolific heavy oil producer in the area since the early 1920’s. It extends from the center of Lake Maracaibo to its eastern shore. The producing reservoirs of this formation are located between 2000 and 5000 feet. Because of the loose and well sorted nature of the sand grains, the porosity tends to be high, ranging from 25 to 40%. Permeability is also high averaging at about 600 md. Here, net oil sands are large and average about 120 ft in thickness. The Eocene Misoa formation lies beneath the center of Lake Maracaibo and along its eastern shores. Fields produce from the sandstone reservoirs at 11000 to 12000 ft. The porosity here ranges from 14 to 20% and the average permeability ranges from 150-400 md. [8]

Traps and Seals

There is a wide variety of structural and stratigraphic traps within this basin. Many of the structural traps were created by the movement of the Caribbean and South American plates. Much of the stratigraphic trapping is due to unconformities and tar plugging while other traps in the basin are a result of transgressional movement along the major faults, which can be seen in Figure 3. The three main fault zones within the basin are the Santa Marta-Bucaramanga fault zone, the Boconó fault zone, and the Oca fault zone which are strike-slip faults that caused the v-shape formation of the basin.[3] The seals in this basin are mainly formed from intraformational mudstones in the Eocene and Miocene sedimentary sections

Figure 3 Seismic time section of the Maracaibo Basin in western Venezuela (Advanced Resources International, Inc., 2013)
Figure 4 Assessment results for three continuous assessment units in the Maracaibo Basin Province, Venezuela and Colombia (U.S. Geological Survey, 2016)

Future Petroleum Potential

The Maracaibo Basin is one of the world’s true super basins, having produced over 30 billion barrels of oil.[1] Due to the geological complexity of the basin, it is likely that there are still many undiscovered pools in the area.[9] Geologist predict that there are many stacked reservoirs with a strike slip nature which can make drilling difficult, but with an increase in exploration of this area and the likeliness of these untouched pools, there is potential for the Maracaibo basin to be highly productive in the future. Figure 4 shows the USGS's assessment of undiscovered recoverable oil and gas resources in the La Luna formation.

Venezuela has been facing a political and socioeconomic crisis and has been seeing a decline in oil exports for over a decade. As of 2020 there has been a halt in searching for oil in Venezuela’s basins and production is very scarce. [10]


Further Reading

Venezuela’s Oil Reserves Doomed To Become The World’s Largest Stranded Asset

Why Does Venezuela Have So Much Oil?

VENEZUELA

References

  1. 1.0 1.1 1.2 1.3 [1]Sutton, F.A. 1946. Geology of Maracaibo Basin, Venezuela 1: PART 1.
  2. [2] Lugo and Mann. (1995). Jurassic-Eocene Tectonic Evolution of Maracaibo Basin, Venezuela
  3. 3.0 3.1 [3]Wikipedia contributors. 2020. Maracaibo Basin. In Wikipedia, The Free Encyclopedia.
  4. [4]AGuzmán, J.I., & Fisher, W.L. (2006). Early and middle Miocene depositional history of the Maracaibo Basin, western Venezuela. AAPG Bulletin, 90, 625-655.
  5. [5]Advanced Resources International, Inc. 2013. EIA/ARI world shale gas and shale oil resources assessment.
  6. 6.0 6.1 [6] U.S. Geological Survey. (1999). World Petroleum Assessment 2000.
  7. [7] U.S. Geological Survey. (2016). Assessment of Continuous Oil and Gas Resources of the Maracaibo Basin Province of Venezuela and Colombia.
  8. [8] Goddard, D. A. 2006. Venezuela sedimentary basins: Principal reservoirs & completion practices.
  9. [9]Rafael Sandrea Martin Essenfeld. 2021. The future of Venezuela’s oil industry.
  10. [10]Wikipedia contributors. 2021. Crisis in Venezuela. Oil Industry. In Wikipedia, The Free Encyclopedia.