U.S. Geological Survey Fact Sheet Fact Sheet FS U.S. Department of the Interior U.S. Geological Survey 2327-69162327-6932 2022-308010.3133/fs20223080 Assessment of Undiscovered Conventional Oil and Gas Resources of the Senegal Basin Province of Northwest Africa, 2021 National and Global Petroleum Assessment 2022 U.S. Geological Survey Reston, Virginia Abstract

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 13,929 million (13.9 billion) barrels of oil and 193,721 billion (193.7 trillion) cubic feet of gas within the Senegal Basin Province of northwest Africa.

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 Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the potential for undiscovered, technically recoverable conventional oil and gas resources within the Senegal Basin Province of northwest Africa (fig. 1). The Senegal Basin Province is one segment of the rifted passive margin that developed along the northwestern margin of Africa as North and South America separated in the Late Triassic. The complex tectonic and stratigraphic evolution of the rifted passive margin from the Triassic to Neogene is reflected in the spectrum of hydrocarbon reservoirs, traps, and source rocks present in the Senegal Basin Province (Brownfield and Charpentier, 2003; Davison, 2005; Ndiaye and others, 2016; Casson and others, 2021).

Map showing the location of one conventional assessment unit (AU) in the Senegal Basin Province, northwest Africa. The Sengal Basin Province boundary coincides with the Senegal Basin Reservoirs AU boundary.

 Total Petroleum System and Assessment Unit

The USGS defined a Mesozoic Composite Total Petroleum System (TPS) that includes organic-rich shales of Triassic to Cretaceous age. Organic-rich Cenomanian–Turonian shales are interpreted as the highest quality source rocks in the basin. They are up to 60 meters thick and have total organic carbon (TOC) values up to 20 weight percent and hydrogen index (HI) values up to 600 milligrams of hydrocarbon per gram of TOC (mg HC/g TOC; Herbin and others, 1986; Nzoussi-Mbassani and others, 2003; Davison, 2005; Wagner and others, 2013; Van Helmond and others, 2014). Organic-rich shales of Aptian–Albian age are up to 100 meters thick and have TOC contents as much as 34 weight percent and HI values that range from 450 to 650 mg HC/g TOC (Hathon, 2018). Geochemical data are not available to characterize neither Triassic synrift lacustrine shales nor Jurassic off-platform, deep-water organic-rich shales.

The Senegal Basin Reservoirs Assessment Unit (AU) was defined to encompass oil and gas that was generated from Triassic to Cretaceous source rocks and migrated into reservoirs within structural and stratigraphic traps. Triassic reservoir rocks may include alluvial, fluvial, deltaic, and lacustrine sandstones within structural and stratigraphic traps, possibly sealed by salt. The margins of salt diapirs and other structures may be sites for sandstone reservoirs sealed by salt. Lower Jurassic to Lower Cretaceous reservoirs may include carbonate platform-margin reefs, karst zones, off-platform sediment gravity flows, and slope-channel and basin-floor sandstones in which clastics have bypassed the carbonate shelf margin (Clayburn, 2018). Upper Cretaceous to Eocene sandstones presently form the most important reservoirs, ranging from fluvial-deltaic to basin-floor fan deposits (Casson and others, 2021). Of these reservoirs, extensive, stacked basin-floor fan sandstones may be the most important reservoir systems for undiscovered resources (Hand and others, 2015; Clayburn, 2018). Key assessment input data are summarized in table 1 and in Schenk (2022).

Key input data for one conventional assessment unit in the Senegal Basin Province, northwest Africa.

[Shading indicates not applicable. AU, assessment unit; MMBO, million barrels of oil; BCFG, billion cubic feet of gas]

Assessment input data—Conventional AUs Senegal Basin Reservoirs AU
Minimum Median Maximum Calculated mean
  Number of oil fields 1   150   300   153.7
  Number of gas fields 1   210   420   215.1
  Size of oil fields (MMBO) 5   10   12,000   90.5
  Size of gas fields (BCFG) 30   72   80,000   647.2
  AU probability 1.0
Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered conventional oil, gas, and natural gas liquid (NGL) resources within the Senegal Basin Province of northwest Africa (table 2). For the Senegal Basin Reservoirs AU, the fully risked mean totals are 13,929 million barrels of oil (MMBO) or 13.9 billion barrels, with an F95–F5 fractile range from 5,749 to 26,079 MMBO; 193,721 billion cubic feet of gas (BCFG), or 193.7 trillion cubic feet, with an F95–F5 range from 87,592 to 342,358 BCFG; and 3,123 million barrels of natural gas liquids (MMBNGL), or 3.1 billion barrels, with an F95–F5 range from 1,401 to 5,554 MMBNGL.

Results for one conventional AU in the Senegal Basin Province, northwest Africa.

[Results shown are fully risked estimates. F95 represents a 95 percent chance of at least the amount tabulated; other fractiles are defined similarly. Shading indicates not applicable. MMBO, million barrels of oil; BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids]

Total petroleum system and assessment units (AUs) AU prob-ability Accum-ulation type Total undiscovered resources
Oil (MMBO) Gas (BCFG) NGL (MMBNGL)
F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean
Mesozoic Composite Total Petroleum System
  Senegal Basin Reservoirs AU   1.0   Oil   5,749   12,748   26,079   13,929   22,433   49,703   101,675   54,324   426   944   1,934   1,032
  Gas   65,159   131,122   240,683   139,397   975   1,965   3,620   2,091
  Total undiscovered conventional resources   5,749   12,748   26,079   13,929   87,592   180,825   342,358   193,721   1,401   2,909   5,554   3,123
For More Information

Assessment results are also available at the USGS Energy Program website, https://www.usgs.gov/energy-and-minerals/energy-resources-program.

 Senegal Basin Province Assessment Team

Christopher J. Schenk, Tracey J. Mercier, Cheryl A. Woodall, Phuong A. Le, Andrea D. Cicero, Ronald M. Drake II, Geoffrey S. Ellis, Thomas M. Finn, Michael H. Gardner, Sarah E. Gelman, Jane S. Hearon, Benjamin G. Johnson, Jenny H. Lagesse, Heidi M. Leathers-Miller, Kristen R. Marra, Kira K. Timm, and Scott S. Young

 References Cited Brownfield, M.E., and Charpentier, R.R., 2003, Assessment of undiscovered oil and gas of the Senegal Province, Mauritania, Senegal, The Gambia, and Guinea-Bissau, northwest Africa: U.S. Geological Survey Bulletin 2207–A, 26 p. [Also available at https://pubs.usgs.gov/bul/b2207-a/.] Casson, M., Calves, G., Huuse, M., Sayers, B., and Redfern, J., 2021, Cretaceous continental margin evolution revealed using quantitative seismic geomorphology, offshore northwest Africa: Basin Research, v. 33, no. 1, p. 66–90. [Also available at https://doi.org/10.1111/bre.12455.] Clayburn, J., 2018, Realizing the deep-water hydrocarbon potential of Senegal: American Association of Petroleum Geologists, Search and Discovery Article No. 70345, 54 p., accessed August 26, 2021, at https://www.searchanddiscovery.com/pdfz/documents/2018/70345clayburn/ndx_clayburn.pdf.html. Davison, I., 2005, Central Atlantic margin basins of northwest Africa—Geology and hydrocarbon potential (Morocco to Guinea): Journal of African Earth Sciences, v. 43, no. 1−3, p. 254–274, accessed August 26, 2021, at https://doi.org/10.1016/j.jafrearsci.2005.07.018. Hand, N., Cilliari, A., Edwards, I., and Jackson, D., 2015, Slope channel complexes offshore North West Africa: GeoExPro, v. 12, no. 4, p. 38–40., accessed August 26, 2021, at https://www.geoexpro.com/articles/2015/10/offshore-mauritania-and-senegal. Hathon, E., 2018, The SNE discovery offshore Senegal—Moving a frontier basin to emergent, in European Association of Geologists and Engineers 80th Annual Conference and Exhibition, Copenhagen, Denmark, June 11–14, 2018, Proceedings: European Association of Geologists and Engineers, 21 p., accessed August 26, 2021, at https://www.earthdoc.org/content/papers/10.3997/2214-4609.201800712. Herbin, J.P., Montadert, L., Muller, C., Gomez, R., Thurow, J., and Wiedmann, J., 1986, Organic-rich sedimentation at the Cenomanian–Turonian boundary in oceanic and coastal basins in the North Atlantic and Tethys, in Summerhayes, C.P., and Shackleton, N.J., eds., North Atlantic Paleoceanography: Geological Society, London, Special Publication 21, p. 389–422. Ndiaye, M., Ngom, P.M., Gorin, G., Villeneuve, M., Sartori, M., and Medou, J., 2016, A new interpretation of the deep-part of the Senegal-Mauritanian Basin in the Diourbel-Theis area by integrating seismic, magnetic, gravimetric, and borehole data—Implications for petroleum exploration: Journal of African Earth Sciences, v. 121, p. 330–341. [Also available at https://doi.org/10.1016/j.jafrearsci.2016.06.002.] Nzoussi-Mbassani, P., Disnar, J.R., and Laggoun-Défarge, F., 2003, Organic-matter characteristics of Cenomanian–Turonian source rocks—Implications for petroleum and gas exploration onshore Senegal: Marine and Petroleum Geology, v. 20, no. 5, p. 411–427. [Also available at https://doi.org/10.1016/S0264-8172(03)00076-X.] Schenk, C.J., 2022, USGS National and Global Oil and Gas Assessment Project—Senegal Basin Province, assessment unit boundaries, assessment input data, and fact sheet data tables: U.S. Geological Survey data release, https://doi.org/10.5066/P9QN4RG5. Van Helmond, N.A.G.M., Ruvalcaba Baroni, I., Sluijs, A., Sinninghe Damste, J.S., and Slomp, C.P., 2014, Spatial extent and degree of oxygen depletion in the deep proto-North Atlantic basin during Oceanic Anoxic Event 2: Geochemistry Geophysics Geosystems, v. 15, no. 11, p. 4254–4266. [Also available at https://doi.org/10.1002/2014GC005528.] Wagner, T., Hofmann, P., and Flogel, S., 2013, Marine black shale deposition and Hadley cell dynamics—A conceptual framework for the Cretaceous Atlantic Ocean: Marine and Petroleum Geology, v. 43, p. 222–238. [Also available at https://doi.org/10.1016/j.marpetgeo.2013.02.005.]