Exploration plays of the Potiguar Basin in deep and ultra-deep water, Brazilian Equatorial Margin
Introduction
The last 15 years have aroused even more the oil prospecting interest on the Brazilian Equatorial Margin basins, due to the significant discoveries in the West Africa Equatorial Margin basins and Guyana-Suriname Basin.
In 2007, the Jubilee play, a giant oil accumulation, was discovered at approximately 3800 m below sea level in the offshore region of Ghana, in the Côte d'Ivoire Sub-basin of Tano Basin. This major discovery caused an exploration interest in the search for new reserves, which culminated in a series of other discoveries, such as Venus (2009), Mercury (2010), and Jupiter (2011) fields in the Sierra Leone-Liberia Basin. Most of these reserves were discovered in Late Cretaceous channels and turbidite fan reservoirs at deep waters, with pinch-out as their main stratigraphic traps, and the source rocks are Cenomanian-Turonian marine shales (Sills and Agyapong, 2012; Tetteh, 2016). Once the African and South American equatorial basins were formed during the fragmentation of the Gondwana supercontinent, they are considered correlated and have similarities in their tectonic-sedimentary evolution (Stolte, 2013). Based on the large discoveries made in West Africa Equatorial Margin, new bidding rounds for blocks in the Brazilian Equatorial Basins were held by the ANP (National Agency of Petroleum, Natural Gas and Biofuels) starting in 2013 and also influenced by discoveries that occurred in the Guiana-Suriname Basin, such as Zaedyus field in 2012. In 2015, ExxonMobil discovered the Liza field in this same basin, in a play similar to Jubilee, with current production of 120,000 bbl/day, and the expectation is about 8 billion barrels of recoverable oil (Baudot et al., 2017; EXXONMOBIL, 2020).
Potiguar Basin (PB) is located at the eastern end of the Brazilian Equatorial Margin, whose correlated basin in the West Africa Equatorial Margin is the Benin Basin, also known as Keta-Benin or Keta-Togo-Benin (Kaki et al., 2013). PB has a history of oil potential in both onshore and offshore, where the onshore region is the most exploited. However, little is still known about the offshore deep and ultra-deep waters regions, which are characterized as an exploratory frontier. So, based on the correlation with the West Africa Equatorial Margin and Guyana-Suriname basins, it is expected that PB may have a great potential for oil and/or gas discoveries in Late Cretaceous to Paleogene turbidite sandstones, with Cenomanian-Turonian shales as source rock.
Section snippets
Geological setting
PB is part of the Brazilian Equatorial Margin basins (Fig. 1) and presents a petroleum exploration history since 1956, with the main oil and gas fields discoveries occurring in the 70s and 80s, both onshore (Fazenda Belém, Canto do Amaro, Estreito, etc.) and offshore shallow waters (Ubarana, Pescada, etc.).
PB tectonic-sedimentary evolution is related to Gondwana supercontinent fragmentation during the Cretaceous and consequent Atlantic Ocean opening. According to Pessoa Neto et al. (2007), its
Dataset and methods
The data were provided by the National Agency of Petroleum, Natural Gas and Biofuels (ANP), consisting of 2D post-stack TWT seismic lines and offshore wells of the PB and Ceará Basin (Fig. 1C). The seismic data comes from two different surveys: R0003_GRAND_NORTH and 0228_2D_SPEC_BM_POT. Besides that, geological and geochemical data of the four deep and ultra-deep water wells of the Potiguar Basin: Well A (1-BRSA-1175-CES), Well B (1-BRSA-1158-CES), Well C (1-BRSA-1205-RNS), and Well D
Seismic interpretation
Five seismic horizons were interpreted in the study area, corresponding to chronostratigraphic markers related to the main basin evolutionary tectonic-sedimentary events: Basement Top (BT - red), middle-Aptian Top (mAT - green), Albian Top (AT - pink), Cretaceous Top (KT - blue) and Oligocene Top (OT - orange), besides the seabed (Recent). In addition, five main units (chronostratigraphic intervals) could be individualized, besides the basement. Fig. 4 summarizes the main characteristics of
Petroleum systems
Trindade et al. (1992), based on the PB source rocks geochemical and molecular characteristics, classified them in two main groups: 1) late Berriasian-early Barremian Pendência Formation lacustrine freshwater shales; and 2) Aptian Alagamar Formation marine evaporitic shales and marls. Alves et al. (2018), when analyzing oils from onshore fields, also identified both these groups.
Based on provided well data geochemical parameters, were here elaborated geochemical logs for wells A, B, C, and D,
Discussion
The correlation of the source and reservoir rocks can be easily observed in Table 4, which presents a summary of the main source and reservoir rocks of the PB, at the Brazilian Equatorial Margin, and the correlated Benin Basin, at the West Africa Equatorial Margin.
The Benin Basin source rocks include late Berriasian-early Barremian (Neocomian) lacustrine shales of the Ise Formation, which its correspondent in the PB is the lacustrine shales of the Pendência Formation (late Berriasian-early
Conclusions
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Five horizons were interpreted, taking into account the main chronostratigraphic markers related to basin tectonic-sedimentary evolution: Basement Top (BT), middle-Aptian (mAT), Albian Top (AT), Cretaceous Top (KT), and Oligocene Top (OT), in addition to the Seabed;
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These horizons limited the following chronostratigraphic intervals: Unit 1 (U1) – BT to mAT, Unit 2 (U2) - mAT to AT, Unit 3 (U3) - AT to KT, Unit 4 (U4) – KT to OT, and Unit 5 (U5) - OT to Seabed;
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The structural analysis
Funding
This work was supported by a one-year scholarship of the PETROBRAS Human Resources Training Program in Geophysics (PFRH-PB-226) and also by the UENF scholarship for completing the MSc dissertation.
Author statements
Ediane Batista da Silva: Formal analysis, Investigation, Methodology, Validation, Data Curation, Investigation, Visualization, Writing-Original Draft, conducted the interpretation work, which was developed during her MSc; Helio Jorge Portugal Severiano Ribeiro: Conceptualization, Methodology, Validation, Investigation, Writing-Original Draft, Writing-Review & Editing, Resources, Supervision, Project administration; Eliane Soares de Souza: Investigation, mainly in Organic Geochemistry,
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The authors thank the Darcy Ribeiro North Fluminense State University (UENF) and the Petroleum Engineering and Exploration Laboratory (LENEP) for the infrastructure and institutional support, the National Agency of Petroleum, Natural Gas and Biofuels (ANP) for the provision of seismic and well data. We also would like to thank the reviewer Juan Pablo Lovecchio for his detailed and constructive suggestions that contributed a lot to the improvement of this manuscript.
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