National and Global Petroleum Assessment 

Assessment of Undiscovered Oil and Gas Resources of 

the Taoudeni Basin Province, Mali and Mauritania, 2015

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3003

March 2016 Printed on recycled paper

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

mean resources of 160 million barrels of conventional oil, 1,880 billion cubic feet of conventional gas, 602 million barrels of 

shale oil, and 6,395 billion cubic feet of shale gas in the Taoudeni Basin Province in Mali and Mauritania.

southwestern part of the basin, yielded 

0.48 million cubic feet of gas per day in 

1974 that was reportedly recovered from 

an infra-Cambrian carbonate reservoir 

(fig. 1; Wenzhe, 2009). Assessment

input data for each assessment unit are 

shown in table 1.

The assessment of continuous 

oil and gas resources by the USGS 

requires that the potential sourcereservoir system must (1) have total

organic carbon contents greater than 

2 weight percent, (2) contain Type I or

Type II organic matter, (3) be within

the oil and gas thermal maturity 

generation window, (4) have organicrich shale greater than 15 meters in 

thickness, and (5) generally occur

at depths greater than 1,500 meters 

(Charpentier and Cook, 2011). Using

these parameters, the USGS defined an

Infra-Cambrian Shale Gas AU within

the Infra-Cambrian Composite TPS and

a Silurian Continuous Oil AU within

the Silurian-Devonian Composite TPS 

(fig. 1). Assessment input data for each

assessment unit are shown in table 1.

Petroleum generation from 

infra-Cambrian source rocks is interpreted to have begun in the Cambrian 

Figure 1. Location of the Taoudeni Basin Province and the four assessment units 

defined in this study. AU, assessment unit. 

Introduction

The objective of the U.S. Geological 

Survey (USGS) National and Global Petroleum

Assessments project is to assess the potential for

undiscovered, technically recoverable oil and 

gas resources within priority geologic provinces 

around the world. As part of this project, the USGS

completed an assessment of the conventional and 

unconventional (continuous) oil and gas resources

of the Taoudeni Basin Province (fig. 1), a complex

province encompassing an area of approximately

1.9 million square kilometers, largely within Mali 

and Mauritania (Villeneuve, 2005). As much as

6 kilometers of infra-Cambrian sedimentary rocks 

(defined here to include sedimentary rocks of

Neoproterozoic and Early Cambrian age) and other

Paleozoic sedimentary rocks are present in the

Taoudeni Basin Province (Waters and Schofield,

2004). It contains five oil and gas exploration wells

(fig. 1) drilled between 1973 and 2011 (IHS Energy,

2014). With this level of exploration, the Taoudeni

Basin Province is considered to be a frontier province (underexplored).

Total Petroleum Systems 

and Assessment Units

The assessment of conventional oil and gas 

resources relies on defining and evaluating potential total petroleum systems (TPS) and the geologic

elements within the TPS. Geologic elements include 

petroleum source rocks (source rock maturation, 

petroleum generation and migration), reservoir rocks

(quality and distribution), and traps for petroleum

accumulations. For the Taoudeni Basin Province, 

the USGS defined an Infra-Cambrian Composite

TPS and an Infra-Cambrian Reservoirs Assessment

Unit (AU) to include infra-Cambrian source rocks

and conventional reservoirs. The Silurian-Devonian 

Composite TPS includes a Lower Paleozoic

Reservoirs AU and is defined by Silurian and minor

Devonian source rocks and Paleozoic conventional

reservoirs. Petroleum shows and limited well-test 

data for the five exploration wells in the province

provide some evidence that these petroleum systems 

exist. For example, the Abolag 1 well, located in the

Ta 8 1

Yarba 1

Ouasa 1

Abolag 1

Atouila 1

MAURITANIA MALI

MOROCCO

ALGERIA

NIGER

GHANA BENIN

NIGERIA

BURKINA FASO

GUINEA

GUINEA

BISSAU

THE GAMBIA

SENEGAL

TOGO

WESTERN SAHARA

ATLANTIC

OCEAN 

Taoudeni Basin Province

EXPLANATION

International boundary

Exploration well identifier

Silurian Continuous Oil AU

Infra-Cambrian Shale Gas AU

Infra-Cambrian Reservoirs AU

Lower Paleozoic Reservoirs AU

28°

24°

16° 12° 8°

20°

16°

12°

4° 0° 4°

0 125 250 MILES

0 125 250 KILOMETERS

ATLANTIC

OCEAN

Area

of study

AFRICA

Source: National Park Service
and continued into the Carboniferous 

prior to the Hercynian orogeny (Wenzhe,

2009). Petroleum generation from

Silurian source rocks possibly began in 

the late Silurian and continued into 

the Carboniferous (Wenzhe, 2009).

Generation ended with the Hercynian

orogeny; uplift and erosion during this

orogeny removed at least 2,400 meters 

of sediment from the central part of the 

basin, possibly influencing the retention

of petroleum in conventional traps or in 

source rocks.

Undiscovered Resource Summary

The USGS quantitatively assessed 

undiscovered oil and gas resources within 

two conventional assessment units and two 

unconventional (continuous) assessment

units within the Taoudeni Basin Province 

(table 2). For conventional resources,

the estimated mean totals for the Lower 

Paleozoic Reservoirs AU are 160 million

barrels of oil (MMBO), 99 billion cubic

feet of gas (BCFG), and 2 million barrels of

natural gas liquids (MMBNGL). Estimated

mean totals for the Infra-Cambrian

Reservoirs AU are 1,781 BCFG and

82 MMBNGL. For continuous resources,

the estimated mean totals for the Silurian 

Continuous Oil AU are 602 MMBO,

361 BCFG, and 6 MMBNGL; the estimated mean totals for the Infra-Cambrian

Shale Gas AU are 6,034 BCFG and

218 MMBNGL. The major source of geologic risk for continuous resources within 

the Taoudeni Basin Province is the retention 

of some part of oil or gas within the source 

rock following any phases of migration.

Table 1. Key assessment input data for the four assessment units of the Taoudeni Basin Province.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million

barrels of natural gas liquids. Well drainage areas and well success ratios are taken from 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 AU Silurian Continuous Oil AU Infra-Cambrian Shale Gas AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 21,500 10,500,000 21,500,000 10,673,833 25,960 13,000,000 25,959,000 12,994,987

Average drainage area of wells (acres) 120 160 200 160 120 160 200 160

Success ratios (%) 5 40 80 41.7 10 40 80 43.3

Average EUR (MMBO, oil; BCFG, gas) 0.01 0.02 0.1 0.024 0.1 0.15 1 0.194

AU probability 0.9 0.9

Assessment input data—Conventional AU Lower Paleozoic Reservoirs AU Infra-Cambrian Reservoirs AU

Number of oil fields 1 25 150 29

Number of gas fields 1 50 400 62

Sizes of oil fields (MMBO) 1 3 150 5

Sizes of gas fields (BCFG) 6 18 600 27

AU probability 0.9 0.9

Table 2. Assessment results for the Taoudeni Basin Province.

[AU, assessment unit; MMBO, million barrels of oil; BCFG, billions of cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked

estimates. For gas accumulations, all liquids are included under the NGL (natural gas liquids) category. F95 represents a 95 percent chance of at least the amount tabulated.

Other fractiles are defined similarly. Fractiles are additive under assumption of perfect positive correlation. Shading indicates not applicable]

Total petroleum system and AU 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

Continuous

resources

Silurian-Devonian Composite Total Petroleum System

Silurian Continuous Oil AU 0.9 Oil 0 475 1,638 602 0 278 1,012 361 0 4 17 6

Infra-Cambrian Composite Total Petroleum System

Infra-Cambrian Shale Gas AU 0.9 Gas 0 4,812 16,182 6,034 0 166 599 218

Total continuous resources 0 475 1,638 602 0 5,090 17,194 6,395 0 170 616 224

Conventional

resources

Silurian-Devonian Composite Total Petroleum System

Lower Paleozoic Reservoirs AU 0.9 Oil 0 135 396 160 0 84 250 99 0 1 4 2

Infra-Cambrian Composite Total Petroleum System

Infra-Cambrian Reservoirs AU 0.9 Gas 0 1,437 4,676 1,781 0 66 218 82

Total conventional resources 0 135 396 160 0 1,521 4,926 1,880 0 67 222 84

Total undiscovered resources 0 610 2,034 762 0 6,611 22,120 8,275 0 237 838 308

References

Charpentier, R.R., and Cook, T.A., 2011, USGS methodology for assessing continuous petroleum resources: U.S. Geological Survey Open-File Report 2011–1167,

75 p. [Also available at http://pubs.usgs.gov/of/2011/1167/.]

IHS Energy, 2014, International petroleum exploration and production database

[current through December 2013]: IHS Energy. [Available from IHS Energy,

15 Inverness Way East, Englewood, CO 80112.]

Villeneuve, Michel, 2005, Paleozoic basins in West Africa and the Mauritanide

thrust belt: Journal of African Earth Sciences, v. 43, nos. 1–3, p. 166–195.

Waters, C.N., and Schofield, D.I., 2004, Contrasting late Neoproterozoic to Ordovician successions of the Taoudeni Basin, Mauritania, and Souss Basin, Morocco: 

Journal of African Earth Sciences, v. 39, nos. 3–4, p. 301–309.

Wenzhe, Gang, 2009, Hydrocarbon generation conditions and exploration potential

of the Taoudeni Basin, Mauritania: Petroleum Science, v. 6, p. 29–37. ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20163003

For Further Information

Assessment results also are available at the USGS Energy

Resources Program Web site at http://energy.usgs.gov.

Taoudeni Basin Province Assessment Team

Michael E. Brownfield, Christopher J. Schenk, Timothy R.

Klett, Marilyn E. Tennyson, Janet K. Pitman, Stephanie B.

Gaswirth, Phuong A. Le, Heidi M. Leathers-Miller, Tracey J.

Mercier, Kristen R. Marra, and Sarah J. Hawkins