National and Global Petroleum Assessment

Assessment of Continuous Oil and Gas Resources of the PutumayoOriente-Marañón Basin Province of Colombia, Ecuador, and Perú, 2018

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

mean resources of 1.1 billion barrels of oil and 793 billion cubic feet of gas in the Putumayo-Oriente-Marañón Basin Province of 

Colombia, Ecuador, and Perú.

Introduction

The U.S. Geological Survey (USGS) quantitatively 

assessed the potential for undiscovered, technically recoverable continuous (unconventional) shale-oil and associated gas 

resources in the Putumayo-Oriente-Marañón Basin Province 

(fig. 1). The development of several petroleum systems in this 

basin is related to the tectonic history of the western margin 

of South America (Wolaver and others, 2015; Calderon and 

others, 2017). Back-arc extension in the Permian and Early 

Triassic formed rift basins with synrift deposits that include 

organic-rich shales of the Permian Ene Formation (Boekhout 

and others, 2018). In the Triassic and Jurassic, back-arc marine 

conditions led to the deposition of organic-rich, carbonate-based 

marine shales of the Pucara Formation (Baby and others, 2006; 

Chalco and Valencia, 2008; Yinfu and others, 2010). In the Late 

Cretaceous, a passive margin existed along a large portion of 

the central and northwestern margin of South America, where 

organic-rich shales of the La Luna Formation and equivalents 

such as the Villeta Shale and Napo Shale were deposited. 

Renewed subduction in the Paleogene led to the formation of a 

complex fold and thrust belt and an adjacent foreland basin on 

the former passive margin (fig. 2). As sediments accumulated 

in the Paleogene foreland basin, organic-rich shales of Permian, 

Triassic–Jurassic, and Late Cretaceous age reached thermal 

maturity for oil generation. Following generation, long-distance 

migration of oil took place from west to east in the Paleogene 

foreland, where source rocks are thermally immature. In the 

PUTUMAYO

BASIN

ORIENTE

BASIN

MARAÑÓN

BASIN

SANTIAGO

BASIN

ECUADOR

COLOMBIA

BRAZIL

PACIFIC

OCEAN

80° W 75° W

0°

5° S

PERÚ

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

A

A' EXPLANATION

Putumayo Basin Villeta Shale Oil AU

Putumayo-Oriente-Marañón Basin 

 Province boundary (part)

Oriente Basin Napo Shale Oil AU

Triassic–Jurassic Pucara Shale Oil AU

Permian Ene Formation Shale Oil AU

A A' Line of section

BRA

VEN

COL

PAN

CRI

ECU

BOL

PACIFIC PER

OCEAN

Map

area

0 100 200 KILOMETERS

0 100 100 MILES

Figure 1. Map showing the location of the four assessment units (AUs) in the Putumayo-Oriente-Marañón Basin Province of Colombia, 

Ecuador, and Perú. Province boundary is from Klett and others, 1997. The three basin names (Putumayo, Oriente, and Marañón) reflect 

country-specific nomenclature.

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2018–3048

September 2018
Neogene, the Cordillera Oriental fold and thrust belt developed 

east of the Paleogene structures, effectively segmenting the 

older foreland (Jacques and others, 2000; Wolaver and others, 

2015; Boekhout and others, 2018). The area of the Neogene 

foreland thus contains only limited areas of thermally mature 

source rock compared to the Paleogene foreland. Much of the 

thermally mature source rock resides in basins west of the 

Cordillera Oriental (Dashwood and Abbotts, 1990).

Total Petroleum Systems and Assessment Units

For continuous oil resources, the USGS defined an Upper 

Cretaceous Total Petroleum System (TPS) with a Putumayo 

Basin Villeta Shale Oil Assessment Unit (AU) and an Oriente 

Basin Napo Shale Oil AU, a Triassic–Jurassic Pucara TPS 

with a Triassic–Jurassic Pucara Shale Oil AU, and a Permian 

Ene Formation TPS with a Permian Ene Formation Shale Oil 

AU. The AUs correspond to those areas that are interpreted 

to have (1) thermally mature source rocks, (2) source rocks 

with greater than 2 weight-percent total organic carbon (TOC), 

and (3) greater than 15 meters of viable source rock. Synrift 

shales of the Permian Ene Formation contain Type I and Type 

II kerogen, have TOC values of as much as 6 weight percent, 

and are as much as 600 meters thick (Mathalone and Montoya, 

1995; Jacques and others, 2000; Brisson and others, 2010; 

Timoteo, 2015; Calderon and others, 2017). Triassic–Jurassic 

Pucara Formation shales contain Type II kerogen, have TOC

values of as much as 14 weight percent, and are as much as

2,000 meters thick (Perupetro, 2003; Yinfu and others, 2010; 

Calderon and others, 2017). Upper Cretaceous Villeta Formation and Napo Formation shales contain Type II and Type IIS 

kerogen, have TOC values of as much as 12 weight percent, 

hydrogen index values of as much as 580 milligrams of hydrocarbon 

per gram of organic carbon, and are as much as 800 meters thick 

(Pinilla and Kairuz, 2006; Chalco and Valencia, 2008; Mancilla 

and others, 2008; Tocco and Hermoza, 2009; Timoteo, 2015; 

Calderon and others, 2017). These organic-rich shales have only 

reached a maximum thermal maturity of peak-oil generation 

in the western part of the present foreland of the PutumayoOriente-Marañón Basin Province. Uncertainty in the assessment 

is largely related to defining the areas of thermally mature 

source rocks with greater than 2 weight percent TOC (Baby and 

others, 2006; Barragan and others, 2013) and to the retention of 

oil within the shales following Neogene deformation.

Assessment input data are summarized in table 1. Input 

data for drainage areas, success ratios, and estimated 

ultimate recoveries are taken from geologic analogs in the 

United States.

Figure 2. Structural cross section across the Marañón Basin, Perú (starting at the Santiago Basin). The assessment units in 

this study are located along the western part of the foredeep belt (from Zhongzhen and others, 2017).

0

−5

5

−10

−15

A A'

SANTIAGO

BASIN

MARAÑÓN BASIN Sub-Andes

thrust belt Foredeep belt Slope belt

Southern uplift

KILOMETERS

Cretaceous

Jurassic

Fault

Basement

Lower Paleozoic

Upper Paleozoic

Triassic

Tertiary

NO VERTICAL EXAGGERATION EXPLANATION

PUTUMAYO-ORIENTE-MARAÑÓN BASIN PROVINCE
Table 1. Key input data for four assessment units (AUs) in the Putumayo-Oriente-Marañón Basin Province of Colombia, Ecuador, and Perú.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery per well; MMBO, million barrels of oil. Well drainage area, success ratio, and EUR are defined 

partly using U.S. shale-oil analogs. Shading indicates not applicable]

Assessment input data—

Continuous AUs

Putumayo Basin Villeta Shale Oil AU Oriente Basin Napo Shale Oil AU

Minimum Mode Maximum Calculated 

mean

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 200 402,500 805,000 402,567 200 1,327,000 2,655,000 1,327,400

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

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

Average EUR (MMBO) 0.01 0.06 0.2 0.067 0.01 0.06 0.2 0.067

AU probability 1.0 1.0

Assessment input data—

Continuous AUs

Triassic–Jurassic Pucara Shale Oil AU Permian Ene Formation Shale Oil AU

Minimum Mode Maximum Calculated 

mean

Minimum Mode Maximum Calculated 

mean

Potential production area of AU (acres) 200 1,005,500 2,011,000 1,055,567 200 3,500,000 13,975,000 5,825,067

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

Success ratio (%) 10 50 90 50 10 30 70 36.7

Average EUR (MMBO) 0.01 0.04 0.1 0.043 0.01 0.04 0.1 0.043

AU probability 1.0 0.6

Table 2. Results for four assessment units (AUs) in the Putumayo-Oriente-Marañón Basin Province of Colombia, Ecuador, and Perú.

[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

Upper Cretaceous Total Petroleum System

Putumayo Basin Villeta Shale Oil AU 1.0 Oil 22 91 267 111 13 54 162 67 0 0 1 0

Oriente Basin Napo Shale Oil AU 1.0 Oil 73 302 869 364 42 179 529 219 0 1 2 1

Triassic–Jurassic Pucara Total Petroleum System

Triassic–Jurassic Pucara Shale Oil AU 1.0 Oil 39 156 397 179 31 124 323 143 0 1 1 1

Permian Ene Formation Total Petroleum System

Permian Ene Formation Shale Oil AU 0.6 Oil 0 282 1,579 455 0 223 1,268 364 0 1 5 1

Total undiscovered continuous 

resources 134 831 3,112 1,109 86 580 2,282 793 0 3 9 3

Undiscovered Resources Summary

The USGS quantitatively assessed shale-oil and associated gas resources in four continuous assessment units 

(table 2) in the Putumayo-Oriente-Marañón Basin Province of Colombia, Ecuador, and Perú. For undiscovered, 

technically recoverable continuous resources, the mean 

totals are 1,109 million barrels of shale oil (MMBO), or 

1.1 billion barrels of oil, with an F95–F5 fractile range 

from 134 to 3,112 MMBO; 793 billion cubic feet of associated gas (BCFG) with an F95–F5 fractile range from 86 to 

2,282 BCFG; and 3 million barrels of natural gas liquids 

(MMBNGL) with an F95–F5 fractile range from 0 to 

9 MMBNGL. Of the mean estimate of 1,109 MMBO, about 

57 percent (634 MMBO) is in the Triassic–Jurassic Pucara 

Shale Oil AU and Permian Ene Formation Shale Oil AU, and 

43 percent (475 MMBO) is in the Putumayo Basin Villeta 

Shale Oil AU and the Oriente Basin Napo Shale Oil AU.

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The original authors’ diacritical mark usage varies for Marañón and 

Perú in this “References Cited” section.

Putumayo-Oriente-Marañón Basin Province Assessment Team 

Christopher J. Schenk, Tracey J. Mercier, Janet K. Pitman, Thomas M. Finn, Phuong A. Le, Stephanie B. Gaswirth, 

Kristen R. Marra, and Heidi M. Leathers-Miller

For More Information

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

ISSN 2327-6916 (print) ISSN 2327-6932 (online) https://doi.org/10.3133/fs20183048