U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2011–3100

August 2011

World Petroleum Resources Project

Assessment of Potential Shale Gas and Shale Oil Resources 

of the Norte Basin, Uruguay, 2011

Printed on recycled paper

Introduction

The U.S. Geological Survey (USGS), in cooperation with the 

U.S. Department of State, is assessing the potential for unconventional oil and gas resources (shale gas, shale oil, tight gas, and 

coalbed gas) in priority geologic provinces worldwide. The authors 

summarize the geologic model and results of an assessment of 

potential shale gas and shale oil resources of the Norte Basin, Uruguay. The Norte Basin of Uruguay is the southern extension of the 

Paraná Basin of Brazil (fig. 1), and is largely covered by volcanic 

rocks. The main geologic structures in the basin are interpreted to 

be northwest-southeast trending grabens and horsts, which, if present, control the distribution of Devonian-age shale and oil and gas 

resources in the basin.

Devonian Shale System in the Norte Basin

The Devonian Cordobes Formation is interpreted to be the 

principal petroleum source rock in the Norte Basin and possible 

reservoir for shale gas and shale oil accumulations. The geologic 

attributes of the Cordobes Formation relevant to the assessment 

are inferred from outcrops along the southern margin of the Norte 

Basin (Conti and Morales, 2009; ANCAP, written commun., 

2011). Thickness of the Cordobes ranges up to 160 meters (m), 

including as much as 60 m of organic-rich shale. Total organic 

carbon concentration ranges from 0.7 to 3.6 weight percent. The 

organic matter is predominantly Type II marine kerogen, with a 

contribution from Type III kerogen. Thermal maturity at outcrop 

averages 0.6 percent vitrinite reflectance, suggesting thermal maturity corresponding to the onset of oil generation. Basin modeling 

suggests that thermal maturity necessary for oil-to-dry gas transition in the Devonian is at a depth of about 3,200 m (ANCAP, 

written commun., 2011), which was used as the boundary 

between potential shale oil and shale gas accumulations in the 

assessment (fig. 1). Given what is known of the thermal maturity, this boundary is uncertain.

Geologic Model for Assessment

The geologic model used in the assessment of the Norte 

Basin assumes oil and gas to have been generated in organic-rich 

shales of the Devonian Cordobes Formation and to occupy matrix 

porosity and organic porosity in the same shales. The thermal 

window for gas was modeled to begin at about the 3,200-m depth, 

with oil as the main petroleum phase at shallower depths. Devonian shales most likely are present beneath the volcanic cover 

in northwest-southeast trending 

grabens that have been imaged 

with geophysical methods. The 

presence of Devonian organic-rich 

shale in the grabens, the potential 

matrix storage of oil or gas, and the 

thermal windows for oil in relation to gas are subject to significant 

geologic uncertainty. Shale gas 

and shale oil accumulations in the 

United States were used as geologic 

and engineering analogs in the 

assessment. Analog data from U.S. 

accumulations included estimated 

ultimate recoveries (EUR) from 

shale gas and shale oil wells, mean 

drainage areas of wells (cell sizes), 

and ranges of well success ratios. 

Key assessment input data are listed 

in table 1.

Using a performance-based geological assessment methodology, 

the U.S. Geological Survey estimated mean volumes of 13.4 trillion 

cubic feet of potential technically recoverable shale gas and 0.5 

billion barrels of technically recoverable shale oil resources in the 

Norte Basin of Uruguay.

30°S

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60°W 59°W 58°W 57°W 56°W 55°W 54°W 53°W 52°W 51°W

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EXPLANATION

Shale gas

Total area

International boundary

Shale oil

Paraná Basin boundary

Norte Basin boundary

Uruguay

River

ATLANTIC

OCEAN

BUENOS

AIRES

Montevideo

Norte 

Basin

Paraná Basin

outcrop

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AMERICA

Figure 1. Locations of the Norte Basin in Uruguay and the areas of the Devonian Cordobes Formation 

Shale Gas Assessment Unit (red) and Devonian Cordobes Formation Shale Oil Assessment Unit (green) 

that were assessed in this study.
Resource Summary

The USGS assessed potential technically recoverable 

shale gas and shale oil resources in the Norte Basin of Uruguay, 

resulting in total estimated mean resources of 13,361 billion 

cubic feet of gas (BCFG), 508 million barrels of oil (MMBO), 

and 499 million barrels of natural gas liquids (MMBNGL) 

(table 2). Of these totals, the estimated mean resource volumes 

are (1) Devonian Cordobes Formation Shale Gas AU, 11,328 

BCFG (range from 0 to 24,042 BCFG), and 453 MMBNGL 

(range from 0 to 1,002 MMBNGL); and (2) for the Devonian 

Cordobes Formation Shale Oil AU, 508 MMBO (range from 

155 to 1,081 MMBO), and 2,033 BCFG associated gas (range 

from 574 to 4,521 BCFG), and 46 MMBNGL (range from 12 to 

106 MMBNGL). The ranges of resource estimates, particularly 

those for shale gas (0 to 24,042 BCFG), reflect the considerable 

geologic uncertainty in these assessment units.

For Further Information

Supporting geologic studies of total petroleum systems and 

assessment units, and reports on the methodology used in the 

Norte Basin assessment, are in progress. Assessment results are 

available at the USGS Energy website: http://energy.usgs.gov

Norte Basin Assessment Team

Christopher J. Schenk, Mark A. Kirschbaum, Ronald R. 

Charpentier, Troy Cook, Timothy R. Klett, Donald L. Gautier, 

Richard M. Pollastro, Jean N. Weaver, and Michael Brownfield.

Acknowledgments

We thank the staff of ANCAP, Montevideo, Uruguay (Hector de Santa Ana Alvarez, Matias Soto Nunez, Josefina Marmisolle Radesca, and Juan Tomasini), for sharing their data and for 

educating us on the petroleum geology of the Norte Basin prior 

to the USGS assessment.

References

Conti, Bruno, and Morales, Ethel, 2009, Geologia y criterios 

exploratorios de la lutitas gasiferas; potencial en el Uruguay: 

Recursos Minerales Energeticos del Uruguay; petroleo, gas, 

hidratos de gas, lutitas bituminosas, carbon, uranio, y almacenamiento de gases: ANCAP Exploracion and Produccion, 

Resumenes de los Trabajos Presentados en la Taller realizado 

en ANCAP, Setiembre 1-2, 2009.

Total petroleum systems 

(TPS) 

and assessment units (AU)

AU

probability

Field 

type

Total undiscovered resources

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

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

Paleozoic Composite TPS

Devonian Cordobes 

Formation Shale Gas AU 0.95 Gas 0 10,306 24,042 11,328 0 402 1,002 453

Devonian Cordobes 

Formation Shale Oil AU 1.0 Oil 155 444 1,081 508 574 1,740 4,521 2,033 12 38 106 46

Total unconventional

 resources 155 444 1,081 508 574 12,046 28,563 13,361 12 440 1,108 499

Table 2. Assessment results for potential shale gas and shale oil resources in the Devonian Cordobes Formation, Norte Basin, 

Uruguay.

[MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids. Results shown are fully risked estimates. 

For gas fields, all liquids are included as NGL (natural gas liquids). Undiscovered gas resources are the sum of nonassociated and associated gas. 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. AU, assessment unit. AU probability is the chance of at least one accumulation of minimum size within the AU. TPS, total petroleum system. 

Gray shading indicates not applicable]

Assessment input data

Devonian Cordobes Shale Gas AU Devonian Cordobes Shale Oil AU

Minimum Mode Maximum Calculated mean Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 271,400 2,714,000 4,071,000 2,352,133 213,200 2,132,000 3,198,000 1,847,700

Average drainage area of wells (acres) 120 150 180 150 100 175 400 225

Average EUR (MMBO, oil; BCFG, gas) 0.2 0.8 2.5 0.89 0.02 0.06 0.25 0.07

Success ratios (%) 75 90 95 87 75 90 95 87

Table 1. Key assessment input data for shale gas and shale oil assessment units in the Norte Basin. 

[EUR (estimated ultimate recovery per well), cell size, and success ratios are from U.S. shale gas and shale oil analogs. MMBO, million barrels of oil; BCFG, 

billion cubic feet of gas; AU, assessment unit; %, percent. Minimum, median, and maximum values represent the variation about the mean values, and do not 

reflect the total variation in these parameters. Areas of AUs are from maps produced by ANCAP, Montevideo, Uruguay.]