Amazonas Basin

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The Amazon Basin, also referred to as the Amazonas Basin, is a sedimentary rich basin that spans across 9 countries: Ecuador, Peru, Brazil, Bolivia, Colombia, Venezuela, French Guiana, Guyana, and Suriname. This basin is rich in crude oil and is so vast that different areas may be referred to with different names. Oil exploration first began in the Western part of the Amazon Basin, Peru and Ecuador, in the 1920s. With a large production boom occurring in the 1970s, many large oil projects followed. However, this has amassed harsh criticism as the Amazon Rainforest is home to indigenous people and thousands of species. In response, National governments have limited areas where hydrocarbon activities can take place. These areas are known as blocks and may be leased to energy companies for exploratory and production purposes.

History of Rock Formation 

Upper Amazonas Basin

The Upper Amazonas Basin is sometimes referred to as the Solimões Basin and is located on the western half of the Amazon and covers an area of approximately 400,000 km2[3]. This area was developed in the late Proterozoic era. This area is subdivided into Jandiatuba and Juruá subbasins. Here, the Juruá gas field and the Urucú oil fields are found. The Urucú oil field produces about 57,000 barrels/day[3]. The Urucu fields produce natural gas and are the largest producing onshore reserves in Brazil[6]. However, the Jandiatuba subbasin has been labelled as not having much potential for hydrocarbon extraction. Also located in the Upper Amazonas Basin is an area called the Vaupes-Amazonas Basin. This area of the basin is located in the southeastern part of Colombia. This section of the Amazon Basin covers 93,000 km2. This area of the Amazon Basin developed in the Precambrian and Paleozoic eras[1]. The Mitu Migmatitic Complex is overlayed by the Piraparana Formation, which is a Proterozoic formation[1]. The Araracuara formation, originating in the Ordovician era, overlays these previously listed formations. The Calizas de Berlin and the upper Permian sandstones represent the upper Paleozoic layers[1].  

Petroleum Geology

Source Rock

Source rocks generate hydrocarbons but need to fit certain parameters to be viable for exploration. The Total Organic Carbon(TOC) should be >1%. Measuring the API Gravity of a formation gives insight into the weight of a petroleum liquid compared to water. Based on this API gravity measure, the petroleum liquid can be further categorized into light, medium, and heavy oil. A light oil will range between 31-55 degrees, medium 22-31 degrees, and heavy is less than or equal to 22 degrees. According to a study by Spigolon, Lewan, de Barros Pentaedo, Coutinho, and Mendonça Filho, the API gravity of 13 samples recovered from the eastern half of the Amazon Basin, had an API gravity range between 22-31 degrees, making this a medium oil. The TOC wt% was found to be 28.5%[8]. This is an extremely strong indication of viable hydrocarbon source rock. After extensive evaluation by Goncalves, Gonzaga, Coutinho, and Triguis, it was found that the Devonian black shales of the Barreirinha, Pitinga, and Curiri Formations are arguably the most important hydrocarbon generators in the Amazon Basin. These shales range from 30m to 160m in thickness and span throughout the Amazon Basin[7].

Reservoir Rock

Reservoir rock is essential for trapping oil. The reservoir rock has to have the appropriate porosity and permeability to allow for migration and accumulation of hydrocarbons. Sandstones found in the Permian Monte Alegre Formation and the Devonian Oriximina Formation form much of the reservoir rock found throughout the Amazon Basin[5].

Trap & Seal

Seismic data and interpretations have indicated a potential for there to be a Late Cretaceous seal over a large portion of the basin[4]. However, a study by Mosmann, Falkenhein, Goncalves, & Nepomuceno has found that the sandstones of the Permian Monte Alegre Formation are thought to be sealed by evaporite strata.

Further Reading

References

1.     Garcia-Gonzales, M., Cruz, L., Mier, R., & Penafort, C. (2009). Hydrocarbon Prospectivity of the Vaupes-Amazonas Basin Colombia. Retrieved December 4, 2022, from https://www.searchanddiscovery.com/abstracts/html/2009/intl/abstracts/garcia.htm.

2.     Gonçalves, F. T. T., F. G. Gonzaga, L. F. C. Coutinho, and J. A. Triguis, 1995, Petroleum geochemistry of the Amazonas Basin, Brazil: oil–source correlation and assessment of hydrocarbon generation and expulsion: Selected Papers, 17th International Meeting on Organic Geochemistry, San Sebastian, p. 444–446.

3.     Kroonenberg, S., & Reeves, C. (2011, December). Geology and Hydrocarbon Potential Vaupes-Amazonas Basin, Colombia. Agencia National de Hidrocarburos. Retrieved December 4, 2022, from https://www.researchgate.net/publication/260096116_Geology_and_hydrocarbon_potential_Vaupes-Amazonas_basin_Colombia

4.     Lauren Penn, P. E. and K. R., Cian O’ Reilly, J. K., & Pat Coole and Craig Koch, P. G.-S. (P. G. S. (2015, August 12). Foz do amazonas basin: Latest exploration enhances prospectivity. GEO ExPro. Retrieved December 6, 2022, from https://www.geoexpro.com/articles/2015/08/foz-do-amazonas-basin-latest-exploration-enhances-prospectivity

5.     Mosmann, R, Falkenhein, F U.H., Goncalves, A, & Nepomuceno, F. Oil and gas potential of Amazon Paleozoic basins. United States.

6.     Nelson, A. (2008, September 29). Exploring Brazil's Urucu natural gas fields sustainably: An impossible task? New Security Beat. Retrieved December 4, 2022, from https://www.newsecuritybeat.org/2008/09/exploring-brazils-urucu-natural-gas-fields-sustainably-an-impossible-task/

7.     Silva, M., Mohriak, W., Holanda, W., Reis, D., & Ferreira, J. (2015, January). Analysis of the Hydrocarbon Maturation Windows in the Amazon Basin. Sociedade Brasileira de Geofísica. Retrieved 2022, from https://sbgf.org.br/mysbgf/eventos/expanded_abstracts/14th_CISBGf/session/BASIN%20ANALYSIS/ANALYSIS%20OF%20THE%20HYDROCARBON%20MATURATION%20WINDOWS%20OF%20THE%20AMAZON%20BASIN.pdf

8.     Spigolon, A., Lewan, M., de Barros Pentaedo, H., Coutinho, L., & Mendonça Filho, J. (n.d.). Evaluation of the petroleum composition and quality with increasing thermal maturity as simulated by hydrous pyrolysis: A case study using a Brazilian source rock with Type I kerogen. Science Direct. Retrieved 2022, from https://www.sciencedirect.com/science/article/abs/pii/S0146638015000443?via%3Dihub.