# Gas hydrate studies in Brazil: future perspectives

Luiz Frederico Rodrigues, João Marcelo Ketzer, José Cupertino, Adolpho Augustin, Daniel Praeg

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Luiz Frederico Rodrigues, João Marcelo Ketzer, José Cupertino, Adolpho Augustin, Daniel Praeg. Gas hydrate studies in Brazil: future perspectives. XVI Latin American Congress on Organic Geochemistry, ALAGO - Associação Latino-Americano de Geoquímica Organica, Aug 2023, Aracaju, Sergipe, Brazil. pp.141-142. hal-04272611

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Submitted on 6 Nov 2023

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# Gas Hydrate Studies in Brazil: Future Perspectives

LUIZ FREDERICO RODRIGUESª, JOÃO MARCELO KETZERᵇ, JOSÉ A. CUPERTINOᶜ, ADOLPHO H. AUGUSTINᶜ, DANIEL PRAEGᵈ

ªUNIVERSIDADE FEDERAL DO RIO GRANDE, ᵇLINNAEUS UNIVERSITY, ᶜUNIVERSIDADE DO VALE DO RIO DOS SINOS, ᵈGEOAZUR

e-mail: luizfrederico.rodrigues@gmail.com

Copyright 2023, ALAGO.

This paper was selected for presentation by an ALAGO Scientific Committee following review of information contained in an abstract submitted by the author(s).

## Introduction

Gas hydrates are energy resources whose organic carbon mass is greater than all other fossil fuels combined and are considered an alternative energy source [1]. In addition to their importance as an energy resource, studies of gas hydrates also provide important information about the Earth's carbon cycle and climate change. Changes in ocean water temperature conditions can cause the dissociation and release of large amounts of methane and carbon dioxide into the atmosphere. Massive destabilization of the gas hydrate system can also cause large underwater mass movements, with potential impact on subsea installations such as oil or even major catastrophes in coastal areas such as generation of tsunamis [2]. The existence of gas hydrates in Brazilian territory was confirmed in the Pelotas Basin [3] and in the Amazon fan [4].

## Experimental

The Amazon deep-sea fan is approximately 250 km from the mouth of the Amazon River and extends 700 km seaward from the outer edge of the continental shelf to water depths of over 4,000 m in the Demerara Abyssal Plain [5]. The Rio Grande Cone is located in the southern portion of the Pelotas Basin and has a water depth between 200 and 3,000 m, 200 km from the city of Rio Grande. It has been deposited since the lower Miocene [6].

## Results and discussion

The gas hydrates from Amazon deep-sea fan present in their composition CH₄ (95%), CO₂ (4%) and C₂H₆ (1%); methane isotope analysis (δ¹³C between -61.7 and -59.2‰ and δD between -206 e -205‰) and ethane (δ¹³C between -31.5 and -30.8‰). These results indicate a biogenic origin with possible thermogenic contamination. This mixing may have occurred during the vertical migration of thermogenic gases through the sediments, until reaching the microbial gas deposits at shallower depths. The thermogenic influence is possibly related to the connection provided by faults connecting deep gas

sources to surface deposits. (Figure 1A). In the Rio Grande Cone, the gas in the hydrate is mostly methane with trace amounts of ethane. Isotopic analysis of methane carbon indicates a microbial origin, whose values varied between δ¹³C from -69,3 to -66,7 (Figure 1B). Likewise, studies of free gases in sediments were produced by the product of microbial methanogenesis, that is, gaseous hydrocarbons were mainly generated by the microbial reduction of CO₂ [7].

<figure><img src="image_2.png" /><figcaption>**Figure 1.** a) Graph showing the relationship between the compositions of C1/(C2+C3) versus ¹³C of gases from hydrates, plumes and gases dissolved in sediments from Amazon deep-sea fan. b) Relationship between the values of δ¹³C₂H₆ e δ¹³CH₄ for samples from different areas of the Rio Grande Cone.</figcaption></figure>

## Conclusion

These discoveries in Brazilian territory aroused the need to carry out additional research that foster the understanding of its occurrence and the future use of this resource in other sedimentary basins. Recently, the works
resulting from these analyzes have aroused the interest
of the world scientific community due to the importance of
hydrates not only as an alternative energy resource but
also for their importance for understanding the carbon
cycle and its impacts on climate change. In the Amazon
deep-sea fan, a cooperation project is being carried out
between Brazilian universities (FURG, PUCRS, UFRGS,
UNISINOS, USP, UFF, UERJ and UFESP), Linnaeus
University, in Sweden, and French research institutes
(IFREMER, GEOAZUR and LSCE). The objective of this
project is to study the past climate history of the equatorial
margin of Brazil over the last million years, to determine
the behavior of gas hydrates in relation to submarine
landslides of great impact and to evaluate the extent of
gas leaks in the Amazon.

Acknowledgment

The authors would like to thank Petrobras S/A for financial
support, Sens Ltda for supporting research and the Pos-
Graduate Program in Technological and Environmental
Chemistry at FURG.

Referências

[1] Collett, T.S.; Johnson, A.H.; Knapp, C.C.; Boswell, R. Natural Gas hydrates: a review. In: Collett, T.; Johnson, A.; Knapp, C.; Boswell, R. (eds.). Natural Gas Hydrates: Energy Resource Potential and Associated Geologic Hazards, AAPG Memoir 89, 2009, p. 146-219.

[2] Mienert, J.; Vanneste, M.; Haflidason, H.; Bünz, S. Norwegian margin outer shelf cracking: a consequence of climate- induced gas hydrate dissociation? Int. J. Earth Sci. (Geol Rundsch) 99 (Suppl. 1), 2010.S207eS225.

[3] Miller, D. J.; Ketzer, J. M.; Viana, A. R.; Kowsmann, R.O.; Freire, A. F. M.; Augustin, A.H.; Lourega, R.V.; Rodrigues, L. F.; Natural gas hydrates in the Rio Grande Cone (Brazil): A new province in the western South Atlantic. Marine and Petroleum Geology, v. 67, 2015, p. 187-196.

[4] Ketzer, J.M.; Augustin, A.; Rodrigues, L.F.; Oliveira, R.; Praeg, D.; Pivel, M.A.; Gas seeps and gas hydrates in the Amazon deep-sea fan. Geo-Marine Letters, v. 38, 2018. 429-438.

[5] Figueiredo, J.; Hoorn, C.; Van der Ven, P.; Soares, E. Late Miocene onset of the Amazon River and the Amazon deep-sea fan: Evidence from the Foz do Amazonas Basin. Geology, 2009, 37, 619-622.

[6] Fontana, R.L.; Mussumeci, A. Hydrates offshore Brazil. In: Annals of the New York Academy of Sciences, International Conference on Natural Gas Hydrates 715, 1994. p. 106 e 113.

[7] Rodrigues, L.F.; Ketzer, J.M.; Oliveira, R.R.; Augustin, A.H.; Cupertino, J.A.; Viana, A.R.; Molecular and isotopic composition of hydrate-bound, dissolved and free gases in the Amazon deep-sea fan and slope sediments, Brazil. Geosciences 9, 2019, 73.
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ANNALS

XVI LATIN AMERICAN CONGRESS ON ORGANIC GEOCHEMISTRY

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ARACAJU 2023

ORGANIZATION:

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ANNALS
XVI LATIN AMERICAN CONGRESS ON ORGANIC GEOCHEMISTRY

Editors:

Alexandre Andrade Ferreira

Alberto Wisniewski Junior

Boniek Gontijo Vaz

Marcelo Corrêa Bernardes

Georgiana Feitosa da Cruz

ISBN n° 978-65-00-75016-4

ARACAJU - SE
2023