U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2019–3016

May 2019

National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources of the Reggane 

Basin Province, Algeria, 2018

Using a geology-based assessment methodology, the U.S. Geological Survey estimated undiscovered, technically recoverable mean resources of 1.3 billion barrels

of oil and 63 trillion cubic feet of gas in the Reggane Basin Province of Algeria.

Introduction

The U.S. Geological Survey (USGS) quantitatively assessed the potential 

for undiscovered, technically recoverable continuous (unconventional) and conventional oil and gas resources in the Reggane Basin Province of Algeria (fig. 1). 

The Reggane Basin is one of a series of North African basins that achieved much 

of their current structural configuration through late Carboniferous−Permian 

(Hercynian orogen) compressional deformation (Boote and others, 1998; Coward 

and Ries, 2003; Badalini and others, 2009). The basin is asymmetric with a steeply 

dipping, structurally complex northeastern margin associated with a sedimentary 

section that gradually thins and shallows to the southwest. Silurian and Devonian 

organic-rich shales are the major petroleum source rocks in the basin (Boote 

and others, 1998). Organic matter in both source rocks may have reached the 

thermal generation window for oil during Carboniferous burial; both source rock 

intervals reached the gas-generation window during the Late Triassic–Jurassic 

(Boote and others, 1998; Logan and Duddy, 1998; Makhous and Galushkin, 

2003; Zuehlke and others, 2010; Jaeger and others, 2017). Only the southwestern 

margin of the basin remains in the oil-generation window (Arab and Djezzar, 

2011). This assessment includes an evaluation of undiscovered continuous (shale 

oil, shale gas, tight gas) resources and conventional oil and gas resources.

Total Petroleum Systems and Assessment Units

The USGS defined a Reggane Silurian Total Petroleum System (TPS) with 

the Reggane Ordovician Tight Gas Assessment Unit (AU), Reggane Silurian 

Shale Gas AU, and Reggane Silurian Shale Oil AU; the Reggane Devonian 

TPS with the Reggane Devonian Shale Gas AU and Reggane Devonian Shale 

Oil AU; and the Silurian–Devonian Composite TPS with the Reggane Conventional Oil and Gas AU. Silurian shales contain 3–5 weight percent residual total 

organic carbon, initial hydrogen index values are as much as 530 milligrams of 

hydrocarbon per gram of total organic carbon, and shale thickness is as much as 

100 meters (Arab and Djezzar, 2011; Kaced and Arab, 2012). Devonian shales 

contain as much as 3 weight percent residual total organic carbon, and shale 

thickness is as much as 80 meters (Kaced and Arab, 2012)

The geologic model for the Silurian TPS is for oil to have been generated 

from organic-rich shales as early as the Carboniferous (Logan and Duddy, 1998), 

and some of this oil was partially retained within the shales in the southwestern 

part of the basin. In much of the basin, oil within the shales cracked to gas possibly during the Late Triassic–Jurassic. Gas may have migrated locally to accumulate 

within subjacent, low-permeability Ordovician sandstones, forming potential 

tight-gas accumulations. The geologic model for the Devonian TPS is similar in 

that oil as well as gas from thermal cracking of oil was partially retained within 

Devonian shales. The geologic model for the Silurian–Devonian Composite TPS 

is for oil and gas from both source rocks to have migrated into conventional 

stratigraphic traps within the basin and into structural traps mainly occurring along 

the faulted northeastern margin of the basin.

Assessment input data are summarized in table 1. For continuous oil and gas 

accumulations, input data for drainage areas, success ratios, and estimated ultimate 

recoveries are taken from geologic analogs in the United States.

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered oil and gas resources in six 

assessment units (table 2). For undiscovered, technically recoverable oil and gas 

resources, the mean totals are 1,296 million barrels of oil (MMBO), or 1.3 billion 

barrels of oil, with an F95–F5 fractile range from 20 to 3,618 MMBO; 63,199 billion 

cubic feet of gas (BCFG), or 63 trillion cubic feet of gas, with an F95–F5 fractile 

range from 13,259 to 147,989 BCFG; and 266 million barrels of natural gas liquids 

(MMBNGL) with an F95–F5 fractile range from 44 to 692 MMBNGL. Of the mean 

total of 1,296 MMBO, 93 percent, or 1,211 MMBO, is continuous oil, and of the 

mean of 63,198 BCFG, 96 percent, or 60,779 BCFG, is continuous gas.

Adrar

Reggane

MOROCCO

ALGERIA

MALI

MAURITANIA

6° W 4° W 2° W 0°

30° N

28° N

26° N

24° N

Base map from U.S. Department of the Interior National Park Service

AFRICA

Map

area

0 50 100 KILOMETERS

0 50 100 MILES

EXPLANATION

Reggane Basin Province boundary

Reggane Silurian Shale Gas AU

Reggane Silurian Shale Oil AU

Reggane Ordovician Tight Gas AU

Reggane Devonian Shale Oil AU

Reggane Conventional Oil and Gas AU

Reggane Devonian Shale Gas AU

References Cited

Arab, M., and Djezzar, S., 2011, Gas potential evaluation of Reggane Basin, southwestern Algeria 

[abs.], in Offshore Mediterranean Conference, Ravenna, Italy, March 23–25, 2011, Proceedings: 

Offshore Mediterranean Conference, Paper OMC-2011-046, accessed November 2, 2018 at 

https://www.researchgate.net/publication/293653456_Gas_Potential_Evaluation_Reggane_

Basin_Southwestern_Algeria_OMC_Conference.

Badalini, G., Redfern, J., and Carr, I.D., 2009, A synthesis of current understanding of the structural evolution of North Africa: Journal of Petroleum Geology, v. 25, no. 3, p. 249–258.

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: The Geological Society of London, Special Publication No. 132, p. 7–68.

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: The Geological Society of London, Special 

Publication No. 207, p. 61–83.

Jaeger, H., Bechstaedt, T., and Mohr, M., 2017, Multi-phase thermal history of Palaeozoic 

basins in NW-Africa (Algeria, Morocco) and its impact on hydrocarbon system development [abs.]: American Association of Petroleum Geologists, Search and Discovery 

Article No. 90313, accessed November 2, 2018, at http://www.searchanddiscovery.com/

abstracts/pdf/2018/90313ar/abstracts/ndx_jaeger.pdf?q=%2BauthorStrip%3Ajaeger.

Figure 1. Map showing the six assessment units (AUs) in the Reggane 

Basin Province, Algeria.
Kaced, M., and Arab, M., 2012, The potential of shale gas plays in Algeria, in 25th World Gas 

Conference, Kuala Lumpur, Malaysia, June 4–8, 2012, Proceedings: International Gas Union, 

18 p., accessed November 2, 2018, at https://www.researchgate.net/publication/282730474_

Shale_gas_potential_of_Algerian_Basins.

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: The Geological Society of London, Special Publication No. 132, p. 131–155.

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: American Association of Petroleum Geologists Bulletin, v. 87, 

no. 11, p. 1799–1822.

Zuehlke, R., Lewandowski, E., Jäger, H., Bechstädt, T., Aicha, R., Wirth, B., and Böckmann, 

M., 2010, Integrated basin and HC systems model, Silurian–Carboniferous, southern 

Algeria: American Association of Petroleum Geologists, Search and Discovery Article No. 

50344, 25 p., accessed October 30, 2018, at http://www.searchanddiscovery.com/pdfz/

documents/2010/50344zuehlke/ndx_zuehlke.pdf.html?q=%252BauthorStrip%253Azuehlke.

Table 1. Key input data for five continuous assessment units (AUs) and one conventional AU in the Reggane Basin Province, Algeria.

[%, percent; EUR, estimated ultimate recovery per well; BCFG, billion cubic feet of gas; MMBO, million barrels of oil. Well drainage area, success ratio, and EUR are defined partly using 

U.S. shale-oil and shale-gas analogs. The average EUR input is the minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Assessment input data—

Continuous AUs

Reggane Ordovician Tight Gas AU Reggane Silurian Shale Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 9,418,000 18,835,000 9,418,000 1,000 9,418,000 18,835,000 9,418,000

Average drainage area of wells (acres) 40 80 120 80 80 120 160 120

Area untested in AU (%) 100 100 100 100 100 100 100 100

Success ratio (%) 10 50 90 50 10 50 90 50

Average EUR (BCFG) 0.08 0.4 1.2 0.440 0.1 0.4 1.3 0.447

AU probability 1.0 1.0

Assessment input data—

Continuous AUs

Reggane Silurian Shale Oil AU Reggane Devonian Shale Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 2,767,000 5,533,000 2,767,000 1,000 9,086,000 18,172,000 9,086,333

Average drainage area of wells (acres) 60 100 120 93.3 80 120 160 120

Area untested in AU (%) 100 100 100 100 100 100 100 100

Success ratio (%) 10 50 90 50 10 50 90 50

Average EUR (MMBO, oil; BCFG, gas) 0.01 0.04 0.2 0.049 0.1 0.4 1.3 0.447

AU probability 0.9 1.0

Assessment input data—

Continuous AU

Reggane Devonian Shale Oil AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 2,476,000 4,951,000 2,476,000

Average drainage area of wells (acres) 60 100 120 93.3

Area untested in AU (%) 100 100 100 100

Success ratio (%) 10 50 90 50

Average EUR (MMBO) 0.01 0.04 0.2 0.049

AU probability 0.9

Assessment input data—

Conventional AU

Reggane Conventional Oil and Gas AU

Minimum Median Maximum Calculated mean

Number of oil fields 1 4 16 4.42

Number of gas fields 1 20 80 22.06

Size of oil fields (MMBO) 5 10 500 19.29

Size of gas fields (BCFG) 30 60 2,000 102.02

AU probability 1.0

Table 2. Results for five continuous assessment units (AUs) and one conventional AU in the Reggane Basin Province, Algeria.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; NGL, natural gas liquids; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. F95 represents a 95-percent chance of at least the amount tabulated; other fractiles are defined similarly. Fractiles are additive under the assumption of perfect positive correlation. Shading indicates 

not applicable]

Total petroleum systems 

and assessment units (AUs)

AU

probability

Accumulation 

type

Total undiscovered resources

Oil (MMBO) Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean F95 F50 F5 Mean

Reggane Silurian Total Petroleum System

Reggane Ordovician Tight Gas AU 1.0 Gas 5,407 21,985 60,150 25,927 17 81 268 104

Reggane Silurian Shale Gas AU 1.0 Gas 3,569 14,462 41,044 17,359 12 53 180 69

Reggane Silurian Shale Oil AU 0.9 Oil 0 494 1,789 641 0 288 1,100 385 0 5 18 6

Reggane Devonian Total Petroleum System

Reggane Devonian Shale Gas AU 1.0 Gas 3,447 14,038 39,694 16,766 11 52 176 67

Reggane Devonian Shale Oil AU 0.9 Oil 0 438 1,604 570 0 256 988 342 0 4 16 5

Total undiscovered continuous resources 0 932 3,393 1,211 12,423 51,029 142,976 60,779 40 195 658 251

Silurian–Devonian Composite Total Petroleum System

Reggane Conventional Oil and Gas AU 1.0

Oil 20 63 225 85 38 123 462 170 0 1 5 2

Gas 798 2,000 4,551 2,250 4 12 29 13

Total undiscovered conventional resources 20 63 225 85 836 2,123 5,013 2,420 4 13 34 15

Total undiscovered resources 20 995 3,618 1,296 13,259 53,152 147,989 63,199 44 208 692 266

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20193016

Reggane Basin Province

Assessment Team

Christopher J. Schenk, Michael E. Brownfield,

Tracey J. Mercier, Cheryl A. Woodall, Phuong A. Le,

Marilyn E. Tennyson, Thomas M. Finn, Kristen R. Marra,

Stephanie B. Gaswirth, Heidi M. Leathers-Miller,

Janet K. Pitman, and Ronald M. Drake II

For More Information

Assessment results are also available at the

USGS Energy Resources Program website at 

https://energy.usgs.gov.