National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources in the Tindouf Basin 

Province, North Africa, 2018

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

2.6 billion barrels of oil and 123.9 trillion cubic feet of gas in the Tindouf Basin Province of North Africa.

Introduction

The U.S. Geological Survey (USGS) completed an assessment of 

undiscovered, technically recoverable conventional and unconventional 

(continuous) oil and gas resources within the Tindouf Basin Province of Algeria, 

Mauritania, Morocco, and Western Sahara (fig. 1). The Tindouf Basin is the 

westernmost of a series of Paleozoic intracontinental basins that are present 

across much of northern Africa (Boote and others, 1998; Badalini and others, 

2002; Dixon and others, 2017). North Africa was a passive margin in the lower 

Paleozoic with fluvial systems flowing northwards towards the ocean. Glaciation 

across North Africa waned in the Ordovician, with meltwater forming a series of 

north-trending incised valleys that were filled with organic-rich sediments during 

a major south-directed transgression in the Silurian (Lüning and others, 2000; 

Le Heron and Craig, 2008). Another major transgression in the Late Devonian 

led to deposition of a second layer of organic-rich shale (Lüning and others, 2003). 

These two potential petroleum source rocks form the foundation of the total 

petroleum systems and assessment units defined and assessed in this study.

Total Petroleum Systems and Assessment Units

The USGS defined three total petroleum systems (TPS) in the Tindouf 

Basin Province. The Silurian TPS contains three assessment units (AUs): 

(1) Tindouf Silurian Shale Gas AU, (2) Tindouf Ordovician Tight Gas AU,

and (3) Tindouf Silurian Shale Oil AU. The Devonian TPS contains the

(1) Tindouf Devonian Shale Gas AU and (2) Tindouf Devonian Shale Oil AU. The 

Silurian–Devonian Composite TPS contains the Tindouf Conventional Oil and 

Gas AU (fig. 1). Silurian shales contain as much as 10 weight percent total 

organic carbon (TOC), hydrogen index (HI) values as much as 380 milligrams 

of hydrocarbon per gram of total organic carbon (mg HC/g TOC), and shale 

thickness is as much as 100 meters (El Diasty and others, 2017). Devonian shales

contain as much as 14 weight percent TOC, HI values are as much as

580 mg HC/g TOC, and shale thickness is as much as 200 meters (Lüning

and others, 2003; Chaouche, 2013).

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

organic-rich shales possibly as early as the Carboniferous (Lüning and others, 2000),

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

of the basin. In the northern part of the basin, oil within the shales cracked to gas

during maturation, and some of the gas was retained within the shales. Gas may

have migrated locally to accumulate into subjacent tight Ordovician sandstones,

forming a potential tight-gas accumulation. 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 following migration. The geologic model for

the Silurian–Devonian Composite TPS is for oil and gas from both source rocks

to have migrated into conventional traps along the structurally complex northern

margin of the basin and into stratigraphic traps within the basin.

Key assessment input data are shown in table 1. Well drainage areas, success ratios, and estimated ultimate recoveries are taken from U.S. shale-oil and

shale-gas analogs. For continuous oil and gas accumulations, zeros at F95 reflect 

the interpretation of geologic risk (AU probability less than 1.0) on the potential 

occurrence of one well of minimum estimated ultimate recoveries in the AU. 

Undiscovered Resources Summary

The USGS quantitatively assessed undiscovered, technically recoverable oil 

and gas resources within six assessment units in the Tindouf Basin Province (table 

2). The estimated total mean resources are 2,575 million barrels of oil 

(MMBO), or 2.6 billion barrels of oil, with an F95 to F5 range from 34 to 

7,176 MMBO; 123,959 billion cubic feet of gas (BCFG), or 123.9 trillion cubic 

feet of gas, with an F95 to F5 range from 2,963 to 316,809 BCFG; and 534 million 

barrels of natural gas liquids (MMBNGL) with an F95 to F5 range from 17 to 

1,480 MMBNGL. Of the mean of 2,575 MMBO, 95 percent, or 2,447 MMBO, 

is continuous oil, and of the mean undiscovered gas resources of 123,959 

BCFG, 93 percent, or 114,928 BCFG, is continuous gas.

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.

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 Publications No. 132, p. 7–68.

Chaouche, A., 2013, Geological and geochemical attributes of Paleozoic source rocks 

and their remaining potential for unconventional resources in Erg Oriental Algerian 

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

80313, 34 p., accessed October 23, 2018, at http://www.searchanddiscovery.com/pdfz/

documents/2013/80313chaouche/ndx_chaouche.pdf.html?q=%252BauthorStrip%253Ac

haouche+-isMeetingAbstract%253Amtgabsyes.

Dixon, R.J., Moore, J.K.S., Bourne, M., Dunn, E., Haig, D.B., Hossack, J., Roberts, N., Parsons, 

T., and Simmons, C.J., 2017, Integrated petroleum systems and play fairway analysis in a 

complex Palaeozoic basin—Ghadames-Illizi Basin, North Africa: The Geological Society of 

London, Petroleum Geology Conference Series, v. 7, p. 735–760.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2019–3006

March 2019

M O R O C C O

M A L I

M A U R I T A N I A

A L G E R I A

Tindouf

ATLANTIC

OCEAN

Agadir

W E S T E R N

S A H A R A

10° W 5° W

30° N

25° N

Map

area

AFRICA

EXPLANATION

0 50 100150 KILOMETERS

0 50 100 150 MILES

Tindouf Silurian Shale Gas AU

Tindouf Ordovician Tight Gas AU

Tindouf Devonian Shale Gas AU

Tindouf Basin Province boundary

Tindouf Devonian Shale Oil AU

Tindouf Conventional Oil and Gas AU

Tindouf Silurian Shale Oil AU

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

Figure 1. Location of the Tindouf Basin Province, North Africa, and the six 

assessment units (AUs) defined in this study.
ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20193006

Table 1. Key input data for six assessment units (AUs) in the Tindouf Basin Province, North Africa.

[AU, assessment unit; %, 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

Tindouf Silurian Shale Gas AU Tindouf Ordovician Tight Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 20,341,000 40,681,000 20,341,000 1,000 20,341,000 40,681,000 20,341,000

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

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) 0.1 0.4 1.3 0.447 0.08 0.4 1.5 0.459

AU probability 0.9 0.9

Assessment input data—

Continuous AUs

Tindouf Silurian Shale Oil AU Tindouf Devonian Shale Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 6,804,000 13,508,000 6,771,000 1,000 16,440,000 32,880,000 16,440,333

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 0.9

Assessment input data—

Continuous AU

Tindouf Devonian Shale Oil AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,000 3,870,000 7,732,000 3,867,667

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

Tindouf Conventional Oil and Gas AU

Minimum Mode Maximum Calculated mean

Number of oil fields 1 6 24 6.62

Number of gas fields 1 50 200 55.13

Size of oil fields (MMBO) 5 10 500 19.29

Size of gas fields (BCFG) 30 60 7,000 158.99

AU probability 1.0

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.

Le Heron, D.P. and Craig, J., 2008, First order reconstructions of a Late Ordovician Saharan 

ice sheet: Journal of the Geological Society [London], v. 165, no. 1, p. 19–29.

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: The Geological Society of London, Special Publications No. 207, p. 165–184.

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.

Tindouf Basin Province 

Assessment Team

Michael E. Brownfield, Christopher J. Schenk, 

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

Marilyn E. Tennyson, Thomas M. Finn, 

Stephanie B. Gaswirth, Janet K. Pitman, Kristen R. Marra, 

Heidi M. Leathers-Miller, 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.

Table 2. Results for six assessment units (AUs) in the Tindouf Basin Province, North Africa.

[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

Silurian Total Petroleum System

Tindouf Silurian Shale Gas AU 0.9 Gas 0 28,316 86,048 33,700 0 103 377 135

Tindouf Ordovician Tight Gas AU 0.9 Gas 0 42,846 138,115 52,334 0 156 606 209

Tindouf Silurian Shale Oil AU 0.9 Oil 0 1,197 4,329 1,554 0 698 2,650 932 0 11 43 15

Devonian Total Petroleum System

Tindouf Devonian Shale Gas AU 0.9 Gas 0 23,027 69,694 27,425 0 84 307 110

Tindouf Devonian Shale Oil AU 0.9 Oil 0 682 2,528 893 0 399 1,554 537 0 6 26 9

Total undiscovered continuous resources 0 1,879 6,857 2,447 0 95,286 298,061 114,928 0 360 1,359 478

Silurian–Devonian Composite Total Petroleum System

Tindouf Conventional Oil and Gas AU 1.0

Oil 34 100 319 128 62 197 655 256 1 2 7 3

Gas 2,901 7,757 18,093 8,775 16 45 114 53

Total undiscovered conventional resources 34 100 319 128 2,963 7,954 18,748 9,031 17 47 121 56

Total undiscovered resources 34 1,979 7,176 2,575 2,963 103,240 316,809 123,959 17 407 1,480 534