U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2016–3086

November 2016

National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources of the Lusitanian 

Basin Province, Portugal, 2016

Printed on recycled paper

Introduction

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

undiscovered, technically recoverable oil and gas resources within the 

Lusitanian Basin Province, a geologically complex area of approximately 20,000 square kilometers along the western margin of Portugal 

(fig. 1). The Lusitanian Basin represents one of the extensional basins 

formed during the initial stages of Mesozoic Tethyan and Atlantic 

rifting that preceded the opening of the north-central segment of the 

Atlantic Ocean. Four phases of Mesozoic extension, two phases of 

Cenozoic compression, and salt movement are recorded in the rocks 

of the Lusitanian Basin, resulting in a complexly structured, compartmentalized basin with several subbasins (Rasmussen and others, 1998; 

Alves and others, 2003; dos Reis and others, 2014a). Organic-rich, 

thermally mature petroleum source rocks are present in (1) Lower 

Jurassic Brenha Formation shales (dos Reis and others, 2014b) and 

possibly present in (2) Silurian shales in the northern part of the basin 

(Uphoff, 2005).

Geologic Models for Assessment

For the Lusitanian Basin Province, the USGS defined the 

Paleozoic–Mesozoic Composite Total Petroleum System (TPS) 

and the Lusitanian Basin Conventional Reservoirs Assessment Unit 

(AU) within this TPS. The geologic model for the assessment is for 

oil and gas generated within Lower Jurassic source rocks during 

the Cretaceous to have migrated into Jurassic carbonate reservoirs 

and Cretaceous clastic reservoirs (dos Reis and others, 2014b). The 

geologic model also includes the potential for oil and gas generated 

from Silurian source rocks possibly during the Late Jurassic, with this 

oil largely cracked to gas and migrated into Triassic synrift clastic 

reservoirs with Jurassic shale seals (Uphoff, 2005). The major source 

of geologic risk in this AU is the possible remigration or loss of oil and 

gas from conventional reservoirs following Cenozoic compression and 

structural inversion. The area of the Lusitanian Basin Conventional 

Reservoirs AU north of the Nazaré Fault displays less effects of compression (Rasmussen and others, 1998), and this area of the AU may 

have less geologic risk than the area south of the fault (fig. 1).

The USGS defined the Lower Jurassic TPS to consist of the 

Brenha Formation Shale Oil AU and the Brenha Formation Shale 

Gas AU. The TPS was defined using thermal maturity, source rock 

thickness, and total organic carbon data from McWhorter and others 

(2014). The geologic model for the assessment is for generation of oil 

and minor gas generated within Brenha Formation source rocks during 

the Cretaceous, with some portion of the oil or gas retained within the 

source rock following two phases of compression and structural inversion in the Cenozoic. The major source of geologic risk in the Brenha 

Formation Shale Oil and Brenha Formation Shale Gas AUs is the 

retention of recoverable oil or gas resources within the source rocks 

following Cenozoic compression.

Assessment input data for each assessment unit are shown 

in table 1. Well drainage areas, estimated ultimate recoveries, and 

success ratios are taken from U.S. shale-oil and shale-gas analogs.

Undiscovered Resource Summary

The USGS quantitatively assessed undiscovered conventional and continuous oil and gas resources within the Lusitanian 

Basin Province (table 2). For total undiscovered resources, the 

estimated means are 121 million barrels of oil (MMBO) with an 

F95–F5 range from 0 to 393 MMBO, 212 billion cubic feet of gas 

(BCFG) with an F95–F5 range from 0 to 723 BCFG, and 12 million barrels of natural gas liquids (MMBNGL) with an F95–F5 

range from 0 to 41 MMBNGL.

LISBON

Setúbal

Coimbra

Santarém

–10° –9°

40°

39°

ATLANTIC OCEAN

PORTUGAL

Source: U.S. Department of the Interior National Park Service

0 25 50 KILOMETERS

0 25 50 MILES

EXPLANATION

Lusitanian Basin Province boundary (part)

Lusitanian Basin Conventional

 Reservoirs AU

Fault—Dashed where location approximate

Brenha Formation Shale Oil AU

Brenha Formation Shale Gas AU

FRANCE

MOROCCO ALGERIA

SPAIN

PORTUGAL

Area of

study

ATLANTIC

OCEAN

NAZARÉ FAULT

Figure 1. Map showing the location of the Lusitanian Basin and the 

three assessment units (AU) defined in this study.

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

resources of 121 million barrels of oil and 212 billion cubic feet of gas in the Lusitanian Basin Province, Portugal.
For total continuous shale-oil resources, the estimated means for the Brenha Formation Shale Oil AU are 66 MMBO with an F95–F5 range 

from 0 to 223 MMBO and 5 BCFG (associated gas) with an F95–F5 range from 0 to 18 BCFG. For shale-gas resources, the estimated means 

for the Brenha Formation Shale Gas AU are 84 BCFG with an F95–F5 range from 0 to 317 BCFG and 4 MMBNGL with an F95–F5 range 

from 0 to 15 MMBNGL. For total undiscovered conventional resources, the estimated means are 55 MMBO with an F95–F5 range from 0 to 

170 MMBO, 123 BCFG with an F95–F5 range from 0 to 388 BCFG, and 8 MMBNGL with an F95–F5 range from 0 to 26 MMBNGL. 

Total petroleum system (TPS) 

and assessment units (AUs)

AU

proability

Accumulation type

Total undiscovered resources

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

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

Paleozoic–Mesozoic Composite TPS

Lusitanian Basin Conventional Resources AU 0.5 Oil 0 36 170 55 0 7 35 11 0 0 1 0

Gas 0 80 353 112 0 5 25 8

Total undiscovered conventional resources 0 36 170 55 0 87 388 123 0 5 26 8

Lower Jurassic TPS

Brenha Formation Shale Oil AU 0.6 Oil 0 43 223 66 0 3 18 5 0 0 0 0

Brenha Formation Shale Gas AU 0.5 Gas 0 0 317 84 0 0 15 4

Total undiscovered continuous resources 0 43 223 66 0 3 335 89 0 0 15 4

Total undiscovered resources 0 79 393 121 0 90 723 212 0 5 41 12

Table 2. Assessment results for two continuous and one conventional assessment unit in the Lusitanian Basin Province, Portugal.

[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 the assumption of perfect positive correlation. Shading indicates not applicable]

For More Information

Assessment results also are available at the USGS Energy 

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

References

Alves, T.M., Gawthorpe, R.L., Hunt, D.W., and Monteiro, J.H., 2003, 

Post-Jurassic tectono-sedimentary evolution of the northern Lusitanian 

Basin (western Iberian margin): Basin Research, v. 15, p. 227–249.

dos Reis, R.P., Pimentel, Nuno, and Garcia, António, 2014a, The evolution of 

the Atlantic margin of Iberia as recorded in the Lusitanian Basin (Portugal): American Association of Petroleum Geologists Search and Discovery 

Article #30370, 21 p., accessed September 15, 2016, at http://www.searchanddiscovery.com/pdfz/documents/2014/30370reis/ndx_reis.pdf.html.

dos Reis, R.P., Pimentel, Nuno, Cardoso, Fátima, and Teixeira, Bernardo, 

2014b, Petroleum systems and thermal modeling of the western Iberian 

margin—From the onshore Lusitanian Basin to the deep offshore Peniche 

Basin: American Association of Petroleum Geologists Search and Discovery 

Article #10679, 25 p., accessed September 15, 2016, at http://www.searchanddiscovery.com/pdfz/documents/2014/10679reis/ndx_reis.pdf.html. 

Table 1. Key assessment input data for two continuous assessment units and one conventional assessment unit in the Lusitanian Basin 

Province, Portugal.

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

EURs, 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 AUs

Brenha Group Shale Oil AU Brenha Group Shale Gas AU

Minimum Mode Maximum Calculated 

mean

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 1,000 563,000 1,876,000 813,333 1,000 127,000 381,000 169,667

Average drainage area of wells (acres) 80 160 240 160 120 160 200 160

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

Average EUR (oil, MMBO; gas, BCFG) 0.01 0.04 0.1 0.043 0.1 0.3 0.7 0.319

AU probability 0.6 0.5

Assessment input data—Conventional AU

Lusitanian Basin Conventional Reservoirs AU

Minimum Mode Maximum Calculated 

mean

Number of oil fields 1 9 30 10

Number of gas fields 1 3 10 3

Sizes of oil fields (MMBO) 5 10 50 11

Sizes of gas fields (BCFG) 30 60 300 68

AU probability 0.5

McWhorter, Sean, Torguson, William, and McWhorter, Ron, 2014, Characterization of the Lias of the Lusitanian Basin, Portugal, as an unconventional resource 

play: American Association of Petroleum Geologists Search and Discovery 

Article #80376, 9 p., accessed September 15, 2016, at http://www.searchanddiscovery.com/documents/2014/80376mcwhorter/ndx_mcwhorter.pdf.

Rasmussen, E.S., Lomholt, Steen, Anderson, Claus, and Vejbaek, O.V., 1998, 

Aspects of the structural evolution of the Lusitanian Basin in Portugal and the 

shelf and slope area offshore Portugal: Tectonophysics, v. 300, p. 199–225.

Uphoff, T.L., 2005, Subsalt (pre-Jurassic) exploration play in the northern 

Lusitanian Basin of Portugal: American Association of Petroleum Geologists Bulletin, v. 89, no. 6, p. 699–714.

ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20163086

Lusitanian Basin Province

Assessment Team

Christopher J. Schenk, Marilyn E. 

Tennyson, Timothy R. Klett, Thomas M. 

Finn, Tracey J. Mercier, Stephanie B. 

Gaswirth, Kristen R. Marra, Phuong A. Le, 

Sarah J. Hawkins, Heidi M. Leathers-Miller, 

and Stanley T. Paxton