U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2015–3085

January 2016

National and Global Petroleum Assessment

Assessment of Unconventional Tight-Gas Resources of the 

Magallanes Basin Province, Chile, 2015

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

of 8.3 trillion cubic feet of unconventional tight gas in the Zona Glauconitica of the Magallanes Basin Province, Chile.

Introduction

The U.S. Geological Survey assesses the 

potential for technically recoverable unconventional shale-oil, shale-gas, tight-oil, tight-gas, 

and coalbed-gas resources in priority geologic 

provinces worldwide. This report summarizes the geologic model and assessment of 

unconventional tight-gas resources within the 

informally defined Zona Glauconitica of the 

Magallanes Basin Province, Chile (fig. 1). The 

Zona Glauconitica is a 50- to 150-meter thick 

transgressive unit consisting of low-permeability 

sandstone and siltstone with significant percentages of glauconite (Zurita and others, 2013). 

Sediments were sourced from the Andean orogen to the west (Biddle and others, 1986). The 

Magallanes Basin Province contains a Lower 

Cretaceous Total Petroleum System made up of 

several source rock intervals containing marine 

Type II organics with as much as 6 weight 

percent total organic matter (Pittion and Arbe, 

1997). Parts of the oil and gas, generated from 

Lower Cretaceous source rocks, (1) migrated 

vertically into the Zona Glauconitica; 

(2) remained in the Lower Cretaceous source 

rocks; and (3) migrated into the underlying 

Springhill Sandstone, which forms the major 

conventional reservoir for more than 200 oil and 

gas fields in the eastern part of the Magallanes 

Basin Province. This study focuses on estimating the potential for technically recoverable 

resources of tight gas in the Zona Glauconitica.

Geologic Model for Assessment

The geologic model used in the assessment of the Zona Glauconitica Tight Gas 

AU (fig. 1) assumes oil and gas were generated within the underlying Lower Cretaceous 

organic rich shales and migrated upward into 

low-permeability transgressive siltstones and 

sandstones of the Zona Glauconitica AU. The 

main phase of migration was oil, which was 

subsequently cracked to condensate and gas in 

the low-permeability reservoir possibly because of elevated heat flow on the 

Springhill Platform. More than 10 wells have tested and produced gas and condensate from the Zona Glauconitica AU, providing evidence of a viable unconventional accumulation. Key assessment input data are summarized in table 1. 

Data for estimated ultimate recovery, well drainage areas, and success ratios 

were derived from comparisons to U.S. analogs for tight-gas reservoirs.

Figure 1. Location of the Magallanes Basin Province in southern Chile and the Zona 

Glauconitica Tight Gas Assessment Unit.

ARGENTINA

ARGENTINA

CHILE

SOUTH 

ATLANTIC OCEAN

MA

GALLANES

STRAIT

71° 70° 69° 68°

52°

53°

SPRINGHILL

PLATFORM

EXPLANATION

International boundary

Zona Glauconitica Tight 

 Gas Assessment Unit

BRAZIL

ARGENTINA

CHILE

BOLIVIA

PARAGUAY

PERU

URUGUAY

FALKLANDS

Area of study

Magallanes Basin

Province

SOUTH

ATLANTIC

OCEAN

SOUTH

PACIFIC

OCEAN

0 20 KILOMETERS

Map image is the intellectual property of Esri and is used herein 0 20 MILES

under license. Copyright © 2015 Esri and its licensors. 

All rights reserved.
ISSN 2327-6916 (print) ISSN 2327-6932 (online) http://dx.doi.org/10.3133/fs20153085

Acknowledgment

We thank Lisandro Rojas G. of Empresa Nacional del 

Petróleo, Santiago, Chile, for providing access to geologic information that allowed us to complete the assessment of tight gas in 

the Zona Glauconitica.

References

Biddle, K.T., Uliana, M.A., Mitchum, R.M., Fitzgerald, M.G., 

and Wright, R.C., 1986, The stratigraphic and structural evolution of the central and eastern Magallanes Basin, southern 

South America: International Association of Sedimentologists, 

Special Publication no. 8, p. 41–61.

Pittion, J.L., and Arbe, H., 1997, Petroleum system in the 

Austral Basin, in Mello, M.R., and Katz, B., eds., Petroleum 

systems of the south Atlantic margins: American Association 

of Petroleum Geologists, Hedberg Research Symposium, Rio 

de Janeiro, Brazil, Extended Abstracts Volume, 3 p.

Magallanes Basin Assessment Team

Christopher J. Schenk, Ronald R. Charpentier, Janet K. Pitman, 

Marilyn E. Tennyson, Michael E. Brownfield, Stephanie B. 

Gaswirth, Phuong A. Le, Heidi M. Leathers-Miller, and 

Kristen R. Marra.

For Further Information

Assessment results also are available at the U.S. Geological 

Survey Energy Resources Program Web site at http://energy.

usgs.gov.

Assessment input data

Zona Glauconitica Tight Gas

Minimum Mode Maximum Calculated

mean

Potential production area of AU (acres) 50,000 750,000 2,300,000 1,033,333

Average drainage area of wells (acres) 60 80 180 107

Success ratios (%) 70 80 90 80

Average EUR (BCFG) 0.6 1.0 1.6 1.025

AU probability 1.0

Table 1. Key assessment input data for the Zona Glauconitica Tight Gas Assessment Unit of the 

Magallanes Basin Province, Chile.

[AU, assessment unit; %, percent; EUR, estimated ultimate recovery; BCFG, billion cubic feet of gas; The EUR per 

well drainage areas and well success ratios are taken from U.S. tight-gas analogs. The average EUR input includes the 

minimum, median, maximum, and calculated mean. Shading indicates not applicable]

Total petroleum system and AU AU

probability

Accumulation 

type

Total undiscovered resources

Gas (BCFG) NGL (MMBNGL)

F95 F50 F5 Mean F95 F50 F5 Mean

Lower Cretaceous Total Petroleum System

Zona Glauconitica Tight Gas AU 1.0 Gas 2,458 7,595 16,290 8,271 23 74 172 83

Total undiscovered unconventional resources 2,458 7,595 16,290 8,271 23 74 172 83

Table 2. Assessment results for tight-gas resources of the Zona Glauconitica Tight Gas Assessment Unit of the Magallanes Basin Province, Chile.

[AU, assessment unit; 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 under the NGL 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]

Unconventional Resource Summary

Total estimated mean tight-gas resource in the Zona Glauconitica AU (fig. 1) is 8,271 billion cubic feet of gas and 83 million barrels of liquids (table 2). The F95–F5 range of resource estimates (2,458 to 16,290 billion cubic feet of gas; 23 to 172 million barrels of 

liquids) reflects considerable geologic uncertainty, particularly with respect to the geologic boundaries of the Zona Glauconitica AU.

Other unconventional oil and gas accumulations might be present in the Magallanes Basin Province, including shale gas and 

shale oil in Lower Cretaceous source rocks and tight gas in deepwater sandstones coeval to the Zona Glauconitica, but these potential 

accumulations were not quantitatively assessed at this time.

Zurita, Enrique, Carpinelli, Aldo, Trejo, Sebastian, and Saa, 

Ariel, 2013, Gas resource potential from Maastrichtian–

Eocene reservoir in Magallanes Basin, Chile: American Association of Petroleum Geologists, International Conference 

and Exhibition, Cartagena, Colombia, September 8–11, 2013, 

Search and Discovery Article no. 90166.