National and Global Petroleum Assessment

Assessment of Undiscovered Oil and Gas Resources in the 

Cuyo Basin Province, Argentina, 2017

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

resources of 236 million barrels of oil and 112 billion cubic feet of associated gas in the Cuyo Basin Province, Argentina.

Introduction

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

assessment of undiscovered, technically recoverable continuous 

(unconventional) and conventional oil and gas resources within 

the Cuyo Basin (or Cuyana Basin) Province of Argentina 

(fig. 1). The Cuyo Basin Province encompasses a group of

Triassic extensional subbasins that formed in a transtensional 

environment as South America began to separate from Africa 

(Uliana and others, 1989; Milani and Fihlo, 2000; Barredo, 

2012; Barredo and others, 2012). The lithologies of the Triassic 

synrift to early postrift sediments of these basins range from 

volcanics to fluvial-lacustrine sandstones and shales. Organicrich lacustrine shales of the late synrift to early postrift Middle 

Triassic Cacheuta Formation are the petroleum source rocks 

in the Cuyo Basin Province (Lopez-Gamundi, 2010; Legarreta 

and Villar, 2011). Andean compression in the Miocene served 

to invert many of the Triassic extensional structures (Dellape 

and Hegedus, 1995), and the resulting foreland orogenic clastic 

wedge buried the lacustrine shales of the Cacheuta subbasin into 

the oil generation window in late Miocene to Pliocene time.

Total Petroleum System and Assessment Units

For the Cuyo Basin Province, the USGS defined the

Triassic Cacheuta Lacustrine Total Petroleum System based on 

the presence and thermal maturation of organic-rich lacustrine 

shales of the Middle Triassic Cacheuta Formation. Organic-rich

lacustrine shales of the Cacheuta Formation are as much as 

400 meters thick, are predominantly Type I organic matter, and 

contain total organic carbon contents up to as much as 10 weight 

percent (Legarreta and Villar, 2011). Shales of the Cacheuta 

Formation are thermally mature with respect to oil generation in 

the Cacheuta subbasin, and nearly all conventional oil fields are

located in this subbasin.

For this assessment, the USGS defined a Cacheuta Subbasin

Lacustrine Shale Oil Assessment Unit (AU), an Alvear Subbasin

Lacustrine Shale Oil AU, and a Cacheuta Subbasin Conventional

Oil AU within the total petroleum system (fig. 1). The geologic

model for the Cacheuta Subbasin Lacustrine Shale Oil AU is for

some portion of recoverable oil to have been retained within the 

Cacheuta Formation lacustrine shales following oil migration 

into conventional traps. The Alvear Subbasin Lacustrine Shale 

Oil AU encompasses the area of the Alvear subbasin (fig. 1).

Lacustrine shales in this subbasin are generally considered to be 

thermally immature with respect to oil generation (Pucci, 2013). 

However, given the uncertainty with the level of thermal maturation, the Alvear Subbasin Lacustrine Shale Oil AU was not quantitatively assessed. The Cacheuta Subbasin Conventional Oil AU

was defined to include oil in conventional reservoirs and traps

that was sourced by lacustrine shales of the Cacheuta Formation. 

The geologic model for this AU is for oil to have migrated from 

lacustrine shales into synrift fluvial and lacustrine sandstones and

into fluvial sandstones of the overlying Rio Blanco Formation

within inverted Triassic extensional structures.

Assessment input data for two AUs are shown in table 1. 

For the Cacheuta Subbasin Lacustrine Shale Oil AU, well drainage areas, estimated ultimate recoveries, and success ratios were 

guided by U.S. shale-oil analogs.

Figure 1. Locations of the Cuyo Basin Province, Argentina, and the 

three assessment units (AUs) defined in this study. The Alvear 

Subbasin Lacustrine Shale Oil AU was not quantitatively assessed.

0 50 100 MILES

0 100 KILOMETERS 50

EXPLANATION

Cuyo Basin Province boundary

Cacheuta Subbasin Lacustrine Shale Oil AU

Alvear Subbasin Lacustrine Shale Oil AU

Cacheuta Subbasin Conventional Oil AU

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

72° 70° 68° 66°

32°

34°

36°

CHILE ARGENTINA

BRA

BOL

URY

PRY

PER

CHL

ARG

COL

VEN GUYSUR

GUF

ECU

SOUTH

ATLANTIC

OCEAN

SOUTH

PACIFIC

OCEAN

Map

area

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2017–3042

July 2017
Undiscovered Resources Summary

The USGS quantitatively assessed technically recoverable, undiscovered conventional and continuous oil and associated gas resources

within the Cuyo Basin Province of Argentina (table 2). For total resources, the estimated means are 236 million barrels of oil (MMBO) with

an F95–F5 range from 55 to 537 MMBO; 112 billion cubic feet of gas (BCFG) with an F95–F5 range from 23 to 266 BCFG; and 1 million

barrels of natural gas liquids (MMBNGL) with an F95–F5 range from 0 to 2 MMBNGL.

Table 1. Key assessment input data for two assessment units (AUs) in the Cuyo Basin Province, Argentina. The Alvear Subbasin Lacustrine 

Shale Oil AU was not quantitatively assessed.

[%, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil. The average EUR input is the minimum, median, maximum, and calculated

mean. Shading indicates not applicable]

Assessment input data—Continuous AU Cacheuta Subbasin Lacustrine Shale Oil AU

Minimum Mode Maximum Calculated mean

Potential production area of AU (acres) 1,600 742,000 1,494,000 745,867

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

Success ratio (%) 10 50 90 50

Average EUR (MMBO) 0.04 0.08 0.3 0.092

AU probability 1.0

Assessment input data—Conventional AU Cacheuta Subbasin Conventional Oil AU

Minimum Median Maximum Calculated mean

Number of oil fields 1 12 24 12.3

Sizes of oil fields (MMBO) 0.5 1.0 35 1.7

AU probability 1.0

Table 2. Assessment results for two assessment units in the Cuyo Basin Province, Argentina.

[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. For gas accumulations, all liquids are included in the NGL 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]

Total petroleum system

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

Triassic Cacheuta Lacustrine Total Petroleum System

Cacheuta Subbasin Lacustrine Shale Oil AU 1.0 Oil 45 182 498 215 21 89 258 108 0 1 2 1

Alvear Subbasin Lacustrine Shale Oil AU Not quantitatively assessed

Total continuous resources 45 182 498 215 21 89 258 108 0 1 2 1

Cacheuta Subbasin Conventional Oil AU 1.0 Oil 10 19 39 21 2 4 8 4 0 0 0 0

Total conventional resources 10 19 39 21 2 4 8 4 0 0 0 0

Total undiscovered resources 55 201 537 236 23 93 266 112 0 1 2 1

References Cited

Barredo, S.P., 2012, Geodynamic and tectonostratigraphic study of a continental rift—The Triassic Cuyana Basin, Argentina, chap. 5 in Sharkov, Eugenii, ed., Tectonics—

Recent advances, accessed April 10, 2017, at https://www.intechopen.com/books/tectonics-recent-advances/geodynamic-and-tectonostratigrafic-study-of-a-continental-riftthe-triassic-cuyana-basin-argentina.

Barredo, S.P.; Chemale, Farid; Marsicano, Claudia; Ávila, J.N.; Ottone, E.G.; and Ramos, V.A., 2012, Tectono-sequence stratigraphy and U–Pb zircon ages of the Rincón 

Blanco depocenter, northern Cuyo rift, Argentina: Gondwana Research, v. 21, nos. 2–3, p. 624–636.

Dellapé, Daniel; and Hegedus, Andrés, 1995, Structural inversion and oil occurrence in the Cuyo Basin of Argentina, in Tankard, A.J., Suárez-Soruco, R., and Welsink, H.J.,

eds., Petroleum basins of South America: American Association of Petroleum Geologists Memoir No. 62, p. 359–367.

Legarreta, Leonardo; and Villar, H.J., 2011, Geological and geochemical keys of the potential shale resources, Argentina basins: American Association of Petroleum Geologists, 

Search and Discovery Article No. 80196, November 11, 2011, 21 p., accessed April 10, 2017, at http://www.searchanddiscovery.com/pdfz/documents/2011/80196legarreta/

ndx_legarreta.pdf.html.

Lopez-Gamundi, Oscar, 2010, Sedimentation styles and variability of organic matter types in the Triassic, non-marine half-grabens of west Argentina—Implications for

petroleum systems in rift basins: Petroleum Geoscience, v. 16, no. 3, p. 267–272.

Milani, E.J., and Fihlo, A.T., 2000, Sedimentary basins of South America, in Cordani, U.G., Milani, E.J., Fihlo, A.T., and Campos, D.A., eds., Tectonic evolution of South America, 

in 31st International Geological Congress,August 6–17, 2000, Rio de Janeiro, Brazil, Proceedings: Secretariat Bureau, 31st International Geological Congress, p. 389–449.

Pucci, J.C., 2013, Argentina’s Alvear subbasin may have unconventional oil: Oil and Gas Journal, July 1, 2013, 30 p., accessed April 10, 2017, at http://www.ogj.com/

articles/print/volume-111/issue-7/exporation-development/argentina-s-alvear-subbasin-may-have.html.

Uliana, M.A., Biddle, K.T., and Cerdan, J., 1989, Mesozoic extension and the formation of Argentine sedimentary basins, in Tankard, A.J., and Balkwill, H.R., Extensional

tectonics and stratigraphy of the North Atlantic margins: American Association of Petroleum Geologists Memoir No. 46, p. 599–614.

For More Information

Assessment results also are available at the USGS Energy Resources Program website at https://energy.usgs.gov.

Cuyo Basin Province Assessment Team

Christopher J. Schenk, Michael E. Brownfield, Marilyn E. Tennyson, Phuong A. Le, Tracey J. Mercier, Thomas M. Finn,

Sarah J. Hawkins, Stephanie B. Gaswirth, Kristen R. Marra, Timothy R. Klett, Heidi M. Leathers-Miller, and Cheryl A. Woodall

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20173042