Exploration plays of the Potiguar Basin in deep and ultra-deep water, Brazilian Equatorial Margin

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Highlights

  • Petroleum geology of the Potiguar Basin, Brazilian Equatorial Margin.

  • Sandy turbidite Late Cretaceous exploration play.

  • Two actives Petroleum Systems for the Cretaceous play.

  • Thermal maturity indicating oil/gas prone source rocks.

Abstract

Following the discoveries on West Africa conjugated margin since 2007 (Jubilee, Tweneboa, Venus, Mercury, and other fields) and in the Guiana-Suriname Basin since 2011 (Zaedyus field and Liza Complex/Exxon's Stabroek block), the Potiguar Basin deep/ultra-deep waters represents one of the most important exploratory frontier basins, like others on the Brazilian Equatorial Margin. Aiming to apply similar plays of these discoveries, was performed a 2D seismic interpretation supported by well data in deep/ultra-deep waters of the Potiguar Basin. Thus, based on the seismic horizons corresponding to the main tectono-sedimentary events, five chronostratigraphic intervals were interpreted: U1, U2, U3, U4, and U5. Moreover, there were interpreted three petroleum systems: Pendência-Pescada (!), Alagamar–Alagamar (!) and Quebradas-Ubarana (.). Pendência Formation source rocks are late Berriasian-early Barremian lacustrine shales. Alagamar Formation source rocks are Aptian-Albian evaporitic marine shales and marls of the Galinhos Member and Ponta do Tubarão Beds. Quebradas Formation source rocks are Cenomanian-Turonian deep water marine shales. Among these source rocks, the best is Galinhos Member/Ponta do Tubarão Beds, reaching up to 21% TOC, Type I, II, and III kerogens, excellent petroleum potential for oil/gas generation, and with thermal maturity at the studied area. Quebradas Formation, which is correlated to Cenomanian-Turonian source rocks of the West Africa Equatorial Margin and Guyana-Suriname basins, reaches up 6% TOC, Type I/II kerogen, very good to excellent petroleum potential for oil generation, and adequate thermal maturity at the studied area. Three plays were interpreted: Strike-slip, Anticlinal, and Late Cretaceous Turbidites, whose water-depth varies from 1,500 m to 1,900 m. Considering the sea bottom as a datum, reservoir rocks (fluvio-deltaic and turbidites sandstones) are about 3,050 m to 5,800 m, and source rocks nearly 3,500 m to 6,500 m. Seal rocks could be Late Cretaceous marine shales. Traps are mainly stratigraphic (pinch-out). Migration pathways are mainly lateral (Late Cretaceous Turbidites play) or also vertical through transtensive faults (Strike-slip and Anticlinal plays). The oil window top estimated depth based on well geochemical profiles is about 2,600 m below the sea bottom. Besides that, studies in West Africa Equatorial Margin basins state the oil window top occurs approximately at 2700 m below the sea bottom. Therefore, all the source rocks to the three interpreted plays are below the oil and/or gas window top. In such a way, the studied area in deep/ultradeep waters of PB has great exploration potential for both oil and/or gas.

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

  • 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;

  • 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;

  • 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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