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Assessment of Undiscovered Shale-Gas Resources in the Grand Erg/Ahnet Basin Province of Algeria, 2026

Fact Sheet 2026-3005
National and Global Petroleum Assessment
By: , , , , , , , , , , and 
https://doi.org/10.3133/fs20263005

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Abstract

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 80.1 trillion cubic feet of shale gas in the Grand Erg/Ahnet Basin Province of Algeria.

Introduction

The U.S. Geological Survey (USGS) assessed the potential for undiscovered, technically recoverable shale-gas resources in the Grand Erg/Ahnet Basin Province of Algeria (fig. 1). The Grand Erg/Ahnet Basin is one of a series of Paleozoic intercratonic basins occupying much of northern Africa (Boote and others, 1998; Badalini and others, 2002; Coward and Ries, 2003; Dixon and others, 2010). During the early Paleozoic, northern Africa was a north-facing passive margin with Ordovician, Devonian, and Silurian siliciclastic depositional systems prograding to the paleo-Tethys Ocean. The Ordovician was a time of regional glaciation in northern Africa, and the retreat of the ice cap and associated large volumes of meltwater formed a series of north-trending incised valleys as much as 200 meters (m) deep that were subsequently filled with organic-rich shales during a major transgression in the early Silurian (Klett, 2000; Lüning and others, 2000; Le Heron and Craig, 2008). A second major transgression in the Late Devonian led to the deposition of organic-rich shales across much of the passive margin. Regional compressional deformation and uplift during the Carboniferous Hercynian orogeny segmented the passive margin into a series of basins—such as the Timimoun, Sbaa, Ahnet, Benoud-Melrhir, Oued Mya, and Mouydir Basins—and adjacent uplifts (Wendt and others, 2006; Eschard and others, 2010; Perron and others, 2018). Uplift and erosion formed the Hercynian unconformity recognized in all northern Africa basins. The focus of this study is on the possible retention of gas within Devonian and Silurian organic-rich shales after uplift, erosion, and possible migration of gas.

Eight assessment units span northern Algeria and southern Morocco.
Figure 1.

Map showing the location of eight shale-gas assessment units (AUs) in the Grand Erg/Ahnet Basin Province of Algeria.

Total Petroleum Systems and Assessment Units

The USGS defined the Devonian Total Petroleum System (TPS) and the Silurian TPS within the Grand Erg/Ahnet Basin Province. The Timimoun Basin Devonian Shale Gas Assessment Unit (AU), Sbaa Basin Devonian Shale Gas AU, and Ahnet Basin Devonian Shale Gas AU were defined within the Devonian TPS. The Benoud-Melrhir Trough Silurian Shale Gas AU, Timimoun Basin Silurian Shale Gas AU, Oued Mya Basin Silurian Shale Gas AU, Sbaa Basin Silurian Shale Gas AU, and Ahnet Basin Silurian Shale Gas AU were defined within the Silurian TPS. Devonian organic-rich shales contain as much as 14 weight percent (wt. pct.) total organic carbon (TOC), have hydrogen index (HI) values as much as 580 milligrams of hydrocarbon per gram of TOC (mg HC/g TOC), and have shale thickness as much as 200 m (Lüning and others, 2003; Chaouche, 2013). Silurian organic-rich shales contain as much as 10 wt. pct. TOC, have HI values as much as 380 mg HC/g TOC, and have shale thickness as much as 100 m (Logan and Duddy, 1998; Kaced and Arab, 2012; El Diasty and others, 2017). Silurian organic-rich shales in the Ahnet Basin are overpressured (Bouchachi and others, 2022), but the regional distribution of overpressure in Devonian or Silurian shales is not known.

The geologic model for the assessment of the Devonian and early Silurian organic-rich shales is for oil and gas to have been generated from organic-rich shales, possibly as early as the Carboniferous (Lüning, and others, 2000; Makhous and Galushkin, 2003; Craig and others, 2010). Oil would have thermally cracked to gas during Mesozoic burial. The basis of the assessment is that some part of the gas was partially retained within the Devonian and Silurian shales after uplift, erosion, and migration to form shale-gas accumulations in the basins. Key assessment input data for the defined AUs are summarized in table 1 and Schenk (2026).

Table 1.    

Key input data for eight shale-gas assessment units in the Grand Erg/Ahnet Basin Province of Algeria.

[Gray shading indicates not applicable. The average estimated ultimate recovery (EUR) input is the minimum, mode, maximum, and calculated mean. AU, assessment unit; %, percent; BCFG, billion cubic feet of gas]
Assessment input data—Continuous AUs Timimoun Basin Devonian Shale Gas AU Sbaa Basin Devonian Shale Gas AU
Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean
Potential production area (acres) 1,000 10,705,000 21,410,000 10,705,333 1,000 1,047,500 2,095,000 1,047,833
Average drainage area (acres) 80 120 160 120 80 120 160 120
Untested area (%) 100 100 100 100 100 100 100 100
Success ratio (%) 10 50 90 50 10 50 90 50
Average EUR (BCFG) 0.1 0.4 1.3 0.447 0.1 0.4 1.3 0.447
AU probability 1.0 1.0
Assessment input data—Continuous AUs Ahnet Basin Devonian Shale Gas AU Benoud-Melrhir Trough Silurian Shale Gas AU
Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean
Potential production area (acres) 1,000 2,931,300 5,862,600 2,931,633 1,000 3,100,000 6,200,000 3,100,333
Average drainage area (acres) 80 120 160 120 80 120 160 120
Untested area (%) 100 100 100 100 100 100 100 100
Success ratio (%) 10 50 90 50 10 50 90 50
Average EUR (BCFG) 0.1 0.4 1.3 0.447 0.1 0.4 1.3 0.447
AU probability 1.0 0.9
Assessment input data—Continuous AUs Timimoun Basin Silurian Shale Gas AU Oued Mya Basin Silurian Shale Gas AU
Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean
Potential production area (acres) 1,000 14,927,000 29,854,000 14,927,333 1,000 5,200,000 10,400,000 5,200,333
Average drainage area (acres) 80 120 160 120 80 120 160 120
Untested area (%) 100 100 100 100 100 100 100 100
Success ratio (%) 10 50 90 50 10 50 90 50
Average EUR (BCFG) 0.1 0.4 1.3 0.447 0.1 0.4 1.3 0.447
AU probability 1.0 0.9
Assessment input data—Continuous AUs Sbaa Basin Silurian Shale Gas AU Ahnet Basin Silurian Shale Gas AU
Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean
Potential production area (acres) 1,000 1,199,500 2,399,000 1,199,833 10,000 5,221,700 10,443,400 5,225,033
Average drainage area (acres) 80 120 160 120 80 120 160 120
Untested area (%) 100 100 100 100 100 100 100 100
Success ratio (%) 10 50 90 50 10 50 90 50
Average EUR (BCFG) 0.1 0.4 1.3 0.447 0.1 0.4 1.3 0.447
AU probability 1.0 1.0
Table 1.    Key input data for eight shale-gas assessment units in the Grand Erg/Ahnet Basin Province of Algeria.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered, technically recoverable shale-gas resources in the Grand Erg/Ahnet Basin Province of Algeria (table 2). The estimated mean resources are 80,109 billion cubic feet of gas (BCFG), or 80.1 trillion cubic feet of gas, with an F95 to F5 range from 13,745 to 191,175 BCFG; and 275 million barrels of natural gas liquids (MMBNGL), with an F95 to F5 range from 39 to 706 MMBNGL.

Table 2.    

Results for eight shale-gas assessment units in the Grand Erg/Ahnet Basin Province of Algeria.

[Gray shading indicates not applicable. Results shown are fully risked estimates. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids]
Total petroleum systems and assessment units (AUs) AU probability Accumulation type Total undiscovered resources
Gas (BCFG) NGL (MMBNGL)
F95 F50 F5 Mean F95 F50 F5 Mean
Timimoun Basin Devonian Shale Gas AU 1.0 Gas 4,095 16,535 46,330 19,784 12 57 186 73
Sbaa Basin Devonian Shale Gas AU 1.0 Gas 396 1,617 4,558 1,936 1 6 18 7
Ahnet Basin Devonian Shale Gas AU 1.0 Gas 1,117 4,501 12,690 5,391 3 14 46 18
Benoud-Melrhir Trough Silurian Shale Gas AU 0.9 Gas 0 4,317 13,053 5,123 0 14 47 17
Timimoun Basin Silurian Shale Gas AU 1.0 Gas 5,696 23,011 64,840 27,438 16 72 230 92
Oued Mya Basin Silurian Shale Gas AU 0.9 Gas 0 7,237 21,736 8,599 0 23 78 29
Sbaa Basin Silurian Shale Gas AU 1.0 Gas 459 1,848 5,242 2,220 1 6 19 7
Ahnet Basin Silurian Shale Gas AU 1.0 Gas 1,982 8,066 22,726 9,618 6 25 82 32
Total undiscovered shale-gas resources 13,745 67,132 191,175 80,109 39 217 706 275
Table 2.    Results for eight shale-gas assessment units in the Grand Erg/Ahnet Basin Province of Algeria.

For More Information

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

Grand Erg/Ahnet Basin Province Assessment Team

Michael E. Brownfield, Christopher J. Schenk, Tracey J. Mercier, Marilyn E. Tennyson, Cheryl A. Woodall, Thomas M. Finn, Phuong A. Le, Heidi M. Leathers-Miller, Janet K. Pitman, Ronald M. Drake II, and Stephanie B. Gaswirth

References Cited

Badalini, G., Redfern, J., and Carr, I.D., 2002, A synthesis of current understanding of the structural evolution of North Africa: Journal of Petroleum Geology, v. 25, no. 3, p. 249–258, accessed February 24, 2026, at https://doi.org/10.1111/j.1747-5457.2002.tb00008.x.

Boote, D.R.D., Clark-Lowes, D.D., and Traut, M.W., 1998, Palaeozoic petroleum systems of North Africa, in Macgregor, D.S., Moody, R.T.J., and Clark-Lowes, D.D., eds., Petroleum geology of North Africa: Geological Society of London Special Publication 132, p. 7–68, accessed February 24, 2026, at https://doi.org/10.1144/GSL.SP.1998.132.01.02.

Bouchachi, Y., Boudella, A., Bourouis, S., Boukhallat, S., and Harbi, A., 2022, In-situ stress analysis of Ahnet Basin, south western Algeria—A 1D geomechanical approach: Journal of African Earth Sciences, v. 196, article 104678, 14 p., accessed February 25, 2026, at https://doi.org/10.1016/j.jafrearsci.2022.104678.

Chaouche, A., 2013, Geological and geochemical attributes of Paleozoic source rocks and their remaining potential for unconventional resources in Erg Oriental Algerian Sahara: AAPG Search and Discovery, article 90163, 34 p., accessed February 24, 2026, at https://www.searchanddiscovery.com/abstracts/html/2013/90163ace/abstracts/chao.htm.

Coward, M.P., and Ries, A.C., 2003, Tectonic development of North African basins, in Arthur, T.J., Macgregor, D.S., and Cameron, N.R., eds., Petroleum geology of Africa—New themes and developing technologies: Geological Society of London Special Publication 207, p. 61–83, accessed February 24, 2026, at https://doi.org/10.1144/GSL.SP.2003.207.4.

Craig, J., Grigo, D., Rebora, A., Serafini, G., and Tebaldi, E., 2010, From Neoproterozoic to Early Cenozoic—Exploring the potential of older and deeper hydrocarbon plays across North Africa and the Middle East, in Vining, B.A., and Pickering, S.C., eds., Petroleum geology—From mature basins to new frontiers—Proceedings of the 7th Petroleum Geology Conference, London, England, March 30–April 2, 2009: Geological Society of London Petroleum Geology Conference Series, v. 7, p. 673–705, accessed February 24, 2026, at https://doi.org/10.1144/0070673.

Dixon, R.J., Moore, J.K.S., Bourne, M., Dunn, E., Haig, D.B., Hossack, J., Roberts, N., Parsons, T., and Simmons, C.J., 2010, Integrated petroleum systems and play fairway analysis in a complex Palaeozoic basin—Ghadames-Illizi Basin, North Africa, in Vining, B.A., and Pickering, S.C., eds., Petroleum geology—From mature basins to new frontiers—Proceedings of the 7th Petroleum Geology Conference, London, England, March 30–April 2, 2009: Geological Society of London Petroleum Geology Conference Series, v. 7, p. 735–760, accessed February 24, 2026, at https://doi.org/10.1144/0070735.

El Diasty, W.S., El Beialy, S.Y., Anwari, T.A., and Batten, D.J., 2017, Hydrocarbon source potential of the Tanezzuft Formation, Murzuq Basin, south-west Libya—An organic geochemical approach: Journal of African Earth Sciences, v. 130, p. 102–109, accessed February 24, 2026, at https://doi.org/10.1016/j.jafrearsci.2017.03.005.

Eschard, R., Braik, F., Bekkouche, D., Ben Rahuma, M., Desaubliaux, G., Deschamps, R., and Proust, J.N., 2010, Palaeohighs—Their influence on the North African Palaeozoic petroleum systems, in Vining, B.A., and Pickering, S.C., eds., Petroleum geology—From mature basins to new frontiers—Proceedings of the 7th Petroleum Geology Conference, London, England, March 30–April 2, 2009: Geological Society of London Petroleum Geology Conference Series, v. 7, p. 707–724, accessed February 24, 2026, at https://doi.org/10.1144/0070707.

Kaced, M., and Arab, M., 2012, The potential of shale gas plays in Algeria—25th World Gas Conference, Kuala Lumpur, Malaysia, June 4–8, 2012: International Gas Union, 18-slide presentation, accessed February 24, 2026, at https://doi.org/10.13140/RG.2.1.4197.4480.

Klett, T.R., 2000, Total petroleum systems of the Grand Erg/Ahnet Province, Algeria and Morocco—The Tanezzuft-Timimoun, Tanezzuft-Ahnet, Tanezzuft-Sbaa, Tanezzuft-Mouydir, Tanezzuft-Benoud, and Tanezzuft-Béchar/Abadla: U.S. Geological Survey Bulletin 2202–B, [144] p., accessed February 24, 2026, at https://doi.org/10.3133/b2202B.

Le Heron, D.P., and Craig, J., 2008, First-order reconstructions of a Late Ordovician Saharan ice sheet: Journal of the Geological Society, v. 165, no. 1, p. 19–29, accessed February 24, 2026, at https://doi.org/10.1144/0016-76492007-002.

Logan, P., and Duddy, I., 1998, An investigation of the thermal history of the Ahnet and Reggane Basins, central Algeria, and the consequences for hydrocarbon generation and accumulation, in Macgregor, D.S., Moody, R.T.J., and Clark-Lowes, D.D., eds., Petroleum geology of North Africa: Geological Society of London Special Publication 132, p. 131–155, accessed February 24, 2026, at https://doi.org/10.1144/GSL.SP.1998.132.01.07.

Lüning, S., Adamson, K., and Craig, J., 2003, Frasnian organic-rich shales in North Africa—Regional distribution and depositional model, in Arthur, T.J., Macgregor, D.S., and Cameron, N.R., eds., Petroleum geology of Africa—New themes and developing technologies: Geological Society of London Special Publication 207, p. 165–184, accessed February 24, 2026, at https://doi.org/10.1144/GSL.SP.2003.207.9.

Lüning, S., Craig, J., Loydell, D.K., Štorch, P., and Fitches, B., 2000, Lower Silurian ‘hot shales’ in North Africa and Arabia—Regional distribution and depositional model: Earth-Science Reviews, v. 49, nos. 1–4, p. 121–200, accessed February 24, 2026, at https://doi.org/10.1016/S0012-8252(99)00060-4.

Makhous, M., and Galushkin, Y.I., 2003, Burial history and thermal evolution of the southern and western Saharan basins—Synthesis and comparison with the eastern and northern Saharan basins: AAPG Bulletin, v. 87, no. 11, p. 1799–1822, accessed February 24, 2026, at https://doi.org/10.1306/06180301123.

Perron, P., Guiraud, M., Vennin, E., Moretti, I., Portier, É., Le Pourhiet, L., and Konaté, M., 2018, Influence of basement heterogeneity on the architecture of low subsidence rate Paleozoic intracratonic basins (Reggane, Ahnet, Mouydir and Illizi basins, Hoggar Massif): Solid Earth, v. 9, p. 1239–1275, accessed February 24, 2026, at https://doi.org/10.5194/se-9-1239-2018.

Schenk, C.J., 2026, USGS National and Global Oil and Gas Assessment Project—Grand Erg/Ahnet Basin Province—Assessment unit boundaries, assessment input data, and fact sheet data tables: U.S. Geological Survey data release, https://doi.org/10.5066/P13BHMMZ.

Wendt, J., Kaufmann, B., Belka, Z., Klug, C., and Lubeseder, S., 2006, Sedimentary evolution of a Palaeozoic basin and ridge system—The Middle and Upper Devonian of the Ahnet and Mouydir (Algerian Sahara): Geological Magazine, v. 143, no. 3, p. 269–299, accessed February 24, 2026, at https://doi.org/10.1017/S0016756806001737.

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Suggested Citation

Brownfield, M.E., Schenk, C.J., Mercier, T.J., Tennyson, M.E., Woodall, C.A., Finn, T.M., Le, P.A., Leathers-Miller, H.M., Pitman, J.K., Drake, R.M., II, and Gaswirth, S.B., 2026, Assessment of undiscovered shale-gas resources in the Grand Erg/Ahnet Basin Province of Algeria, 2026: U.S. Geological Survey Fact Sheet 2026–3005, 4 p., https://doi.org/10.3133/fs20263005.

ISSN: 2327-6932 (online)

Study Area

Publication type Report
Publication Subtype USGS Numbered Series
Title Assessment of undiscovered shale-gas resources in the Grand Erg/Ahnet Basin Province of Algeria, 2026
Series title Fact Sheet
Series number 2026-3005
DOI 10.3133/fs20263005
Publication Date April 22, 2026
Year Published 2026
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Central Energy Resources Science Center
Description Report: 4 p.; Data Release
Country Algeria
Other Geospatial Grand Erg/Ahnet Basin Province
Online Only (Y/N) Y
Additional publication details