Assessment of Undiscovered Oil and Gas in the Arctic

Abstract

Among the greatest uncertainties in future energy supply and a subject of considerable environmental concern is the amount
of oil and gas yet to be found in the Arctic. By using a probabilistic geology-based methodology, the United States Geological
Survey has assessed the area north of the Arctic Circle and concluded that about 30% of the world’s undiscovered gas and 13%
of the world’s undiscovered oil may be found there, mostly offshore under less than 500 meters of water. Undiscovered natural
gas is three times more abundant than oil in the Arctic and is largely concentrated in Russia. Oil resources, although important
to the interests of Arctic countries, are probably not sufficient to substantially shift the current geographic pattern of
world oil production.

Full text

DOI: 10.1126/science.1169467
, 1175 (2009); 324Science et al.Donald L. Gautier,
Arctic
Assessment of Undiscovered Oil and Gas in the
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the shallower part. In the southern Mariana, dif-
ferential slab dip between two adjacent segments
has been detected and attributed to slab tear (24).
We for the first time report the slab tear and con-
sequent slab gap associated with slab stagnation.
The process of slab tearing should reflect the
subduction history of the Pacific plate. Paleogeo-
graphic reconstruction models indicate that the
Izu-Bonin trench migrated eastward with a clock-
wise rotation between the mid-Eocene and late
Miocene, leading to the eastward migration of the
junction of the Izu-Bonin and Japan trenches
(25–27). This migration of the trench–trench
junction implies an eastward migration of the tip
of the slab gap, which should have been syn-
chronous with the westward advance of the lead-
ing edge of the flattened part of the Izu-Bonin
slab. Thus, the slab gap has extended over time
both to the west and to the east.
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28. We thank the National Research Institut e for Earth
Science and Di saster Prevention for providing
Japan-Indonesia Seismic N etwork, South Pacific
Broadband Seismic Network , and Hi-net data.
We are grateful to B. L. N. Kennett for use of SKIPPY
data and to Incorporated Research Institutions for
Seismology for use of their broadband network data.
This study was supported by Grants -in-Aid for Sc ience
Research in the Priority Areas of “St agnant Slab:
A New Keyword for Mantle Dynamics”(16075208).
Supporting Online Material
www.sciencemag.org/cgi/content/full/324/5931/1173/DC1
SOM Text
Figs. S1 to S8
References
18 February 2009; accepted 23 April 2009
10.1126/science.1172496
Assessment of Undiscovered Oil and
Gas in the Arctic
Donald L. Gautier,
1
*Kenneth J. Bird,
1
Ronald R. Charpentier,
2
Arthur Grantz,
3
David W. Houseknecht,
4
Timothy R. Klett,
2
Thomas E. Moore,
1
Janet K. Pitman,
2
Christopher J. Schenk,
2
John H. Schuenemeyer,
5
Kai Sørensen,
6
Marilyn E. Tennyson,
2
Zenon C. Valin,
1
Craig J. Wandrey
2
Among the greatest uncertainties in future energy supply and a subject of considerable environmental
concern is the amount of oil and gas yet to be found in the Arctic. By using a probabilistic geology-
based methodology, the United States Geological Survey has assessed the area north of the Arctic
Circle and concluded that about 30% of the world’sundiscoveredgasand13%oftheworld’s
undiscovered oil may be found there, mostly offshore under less than 500 meters of water.
Undiscovered natural gas is three times more abundant than oil in the Arctic and is largely
concentrated in Russia. Oil resources, although important to the interests of Arctic countries, are
probably not sufficient to substantially shift the current geographic pattern of world oil production.
Among the greatest uncertainties concern-
ing future energy supply is the volume of
oil and gas remaining to be found in high
northern latitudes. The potential for resource
development is of increasing concern to the Arctic
nations, to petroleum companies, and to all
concerned about the region’s fragile environments.
These concerns have been heightened by the
recent retreat of polar ice, which is changing
ecosystems and improving the prospect of easier
petroleum exploration and development. For
better or worse, limited exploration opportunities
elsewhere in the world combined with techno-
logical advances make the Arctic increasingly
attractive for development. To provide a perspec-
tive on the oil and gas resource potential of the
region, the U.S. Geological Survey (USGS) com-
pleted a geologically based assessment of the
Arctic, the Circum-Arctic Resource Appraisal
(CARA), which exists entirely in the public domain.
Of the 6% of Earth’s surface encompassed by
the Arctic Circle, one-third is above sea level and
another third is in continental shelves beneath less
than 500 m of water. The remainder consists of
deep ocean basins historically covered by sea ice.
Many onshore areas have already been explored;
by 2007, more than 400 oil and gas fields,
containing 40 billion barrels of oil (BBO), 1136
trillion cubic feet (TCF) of natural gas, and 8 billion
barrels of natural gas liquids had been developed
Fig. 4. (Ato F)Cross
sections of the Pwave
speed anomalies along
meridians from 134°E to
139°E at one-degree in-
tervals. The depth range
is from the surface to
800 km. A red line seg-
ment in (C) indicates the
S-to-Pconversion plane.
The profiles for (A) and
(F)areshowninFig.1B.
S
2.0% fastslow 2.0%
N
A
B
C
D
E
F
139°E
138°E
137°E
136°E
135°E
134°E
S-P conversion
interface
1
U.S. Geological Survey, 345 Middlefield Road, Menlo Park,
CA 94025, USA.
2
U.S. Geological Survey, Box 25046 Federal
Center, Denver, CO 80225, USA.
3
930 Van Auken Circle, Palo
Alto, CA 94303, USA.
4
U.S. Geological Survey, 12201 Sunrise
Valley Drive, Reston, VA 20192, USA.
5
Southwest Statistical
Consulting, 960 Sligo Street, Cortez, CO 81321, USA.
6
Geological Survey of Denmark and Greenland, Øster
Voldgade 10, DK-1350 Copenhagen K Denmark.
*To whom correspondence should be addressed. E-mail:
gautier@usgs.gov
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north of the Arctic Circle, mostly in the West Sibe-
rian Basin of Russia and on the North Slope of
Alaska (1).
Deep oceanic basins have relatively low pe-
troleum potential, but the Arctic continental shelves
constitute one of the world’s largest remaining
prospective areas. Until now, remoteness and
technical difficulty, coupled with abundant low-
cost petroleum, have ensured that little exploration
occurred offshore. Even where offshore wells have
been drilled, in the Mackenzie Delta, the Barents
Sea, the Sverdrup Basin, and offshore Alaska, most
resulting discoveries remain undeveloped.
The CARA only considered accumulations with
recoverable hydrocarbon volumes larger than 50
million barrels of oil or 300 billion cubic feet of gas
(50 million barrels of oil equivalent, 50 MMBOE)
(2). Smaller accumulations were excluded as were
nonconventional resources such as coal bed meth-
ane, gas hydrates, oil shales, and heavy oil and tar
sands. Geological risk was explicitly assessed, but
technological and economic risks were not.
Resources were assumed to be recoverable even in
the presence of sea ice or oceanic water depths.
Initial results are presented without reference to costs
of exploration and development.
Petroleum is overwhelmingly associated with
sedimentary rocks. Therefore, a new map was
assembled to delineate the Arctic sedimentary
successions by age, thickness, and structural and
tectonic setting (3). The map provided the basis
for defining assessment units (AUs), which are
mappable volumes of sedimentary rocks that
share similar geological properties. The CARA
defined 69 AUs (4), each containing more than
3 km of sedimentary strata, the probable mini-
mum thickness necessary to bury petroleum source
rocks sufficiently to generate significant petro-
leum. Areas outside the 69 AUs were interpreted
to have low petroleum potential.
Geologic information about each AU was
compiled from published literature and from data
made available by cooperating organizations, in-
cluding the Bundesanstalt für Geowissenschaften
und Rohstoffe, the Geological Survey of Canada,
the Geological Survey of Denmark and Green-
land, the Norwegian Petroleum Directorate, and
the U.S. Minerals Management Service. Many
active industry petroleum geologists also gener-
ously shared concepts and data. Although many
organizations and individuals contributed to the
geological analysis, the numerical assessments
are the sole responsibility of the USGS.
The study relied on a probabilistic method-
ology of geological analysis and analog modeling
(2). Burial history-fluid evolution models were
prepared with use of standard modeling software
such as PetroMod (http://www.petromod.com/) and
BasinMod (www.platte.com/). On the basis of the
presence and maturity of source rock, migration
pathways, reservoir, and trap and seal, geologists
postulated the presence of petroleum systems for
review by the CARA team. Analogs were derived
from a world database of 246 AUs previously
defined for the USGS World Petroleum Assess-
ment 2000 (5). The 246 AUs, which account for
Fig. 1. Map showing the AUs of the CARA is color-coded for mean estimated undiscovered oil. Only areas north of the Arctic Circle are included in the
estimates. AU labels are the same as in table S1. Black lines indicate AU boundaries.
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more than 95% of known oil and gas outside the
United States, were classified according to
geologic parameters such as age of source rocks,
structural style, and tectonic setting (6). With
use of data from IHS Incorporated (1), we
identified oil and gas fields in each of the 246
AUs and used them to compile global distribu-
tions for field sizes, field densities (fields per
1000 km
2
), and other parameters.
The CARA team analyzed each Arctic AU to
determine the geologic properties most likely to
control the sizes and numbers of undiscovered
petroleum accumulations. Families of AUs from
the analog database with similar geologic properties
were identified. For example, the assessment units
of northeastern Greenland exhibit the geologic
features of rift-sag basins and rifted passive
continental margins. Accordingly, for the assess-
ment of northeastern Greenland, groups of analogs
were selected from the world’s population of rift-
sag basins and rifted passive margins. In most
cases, field data from these populations of analogs
provided numerical information for the assessment.
The marginal (unconditional) probability that at
least one undiscovered accumulation greater than
minimum size (>50 MMBOE) exists within the AU
was assessed on the basis of three geologic elements:
charge, including source rocks and thermal maturity;
rocks, including reservoirs, traps, and seals; and
timing, including the relative ages of migration and
trap formation, as well as preservation.
The marginal probability of each AU was
calibrated against a ranked list of all other CARA
AUs. Only CARA AUs with known accumu-
lations were assigned a probability of 1; AUs
with <0.1 probability were not quantitatively
assessed (table S1). Worldwide, 50 to 60% of
similarly defined AUs contain at least one ac-
cumulation >50 MMBOE (7). However, the re-
sulting mean of assessed AU probabilities in this
study is about 41%, significantly less than the
global average. This difference reflects the geo-
logic judgment of the CARA team that the pe-
troleum potential of the Arctic differs somewhat
from the global population of petroleum basins.
Given the presence of at least one accumulation,
three conditional distributions were assessed for each
AU: the numbers of undiscovered accumulations,
the size frequency of undiscovered accumulations,
and the likelihood of oil versus gas in each accumu-
lation. The three conditional distributions were
combined in a Monte Carlo simulation of 50,000
trials. Forty-nine of the 69 AUs were quantitatively
assessed. Quantitative results of the CARA are listed
in table S1 and illustrated in Figs. 1 and 2.
Individual AU assessments were statistically ag-
gregated into Circum-Arctic totals, taking into
account partial correlations between AUs with geo-
logic similarities (2,8). The CARA results suggest
there is a high probability (>95% chance) that more
than 44 BBO, a one in two chance (50%) that more
than 83 BBO, and a 1 in 20 chance (5%) that as
much as 157 BBO could be added to proved
Fig. 2. Map showing the AUs of the CARA is color-coded for mean estimated undiscovered gas. Only areas north of the Arctic Circle are included in the
estimates. AU labels are the same as in table S1. Black lines indicate AU boundaries.
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reserves from new oil discoveries north of the Arctic
Circle. Correlation increases the spread in estimated
aggregate volume compared with an assumption of
geologic independence. A perfect positive correla-
tion, although geologically unreasonable, would
yield the widest spread of aggregate volumes. If per-
fect positive correlation among all AUs were
assumed, the estimated volume of undiscovered oil
would range from about 22 BBO to about 256 BBO.
The mean estimate is more than double the
amount of oil that has previously been found in the
Arctic. For comparison, at the end of 2007, world
proved reserves of oil, excluding Canadian oil
sands, stood at about 1238 BBO and consumption
was about 30 BBO per year (9). On the basis of the
USGS World Petroleum Assessment 2000 (5)
adjusted for discoveries since 1996, the Arctic may
contain about 13% of the mean estimated global
undiscovered oil resource of about 618 BBO.
Assuming reserves in existing fields will increase
by an additional 400 BBO, undiscovered oil in the
Arctic may account for almost 4% of the world’s
remaining conventionally recoverable oil resources.
All 49 assessed AUs were estimated to contain
undiscovered oil, but 60% of the resource is
concentrated in just six of them. The Alaska
Platform stands out (Fig. 3), with more than 31%
of mean undiscovered Arctic oil (27.9 BBO). Other
important AUs include the Canning-Mackenzie (6.4
BBO),NorthBarentsBasin(5.3BBO),Yenisey-
Khatanga (5.3 BBO), Northwest Greenland Rifted
Margin (4.9 BBO), and two AUs on the northeast
Greenland Shelf: South Danmarkshavn Basin (4.4
BBO) and the North Danmarkshavn Salt Basin (3.3
BBO). The Alaska Platform is already a well-
known petroleum-producing area; new discoveries
there could maintain the flow of Alaskan oil for
many years to come. Oil discoveries in the other
areas could change the economic landscape and
way of life of local inhabitants. However, the
estimated resource is probably not sufficient to shift
the world oil balance. Moreover, the estimated oil
resources, if found, would not come into production
at once but rather be added to reserves and produced
incrementally.
On an energy-equivalent basis, we estimate that
the Arctic contains more than three times as much
undiscovered gas as oil. The estimated largest
undiscovered gas accumulation is almost eight times
the estimated size of the largest undiscovered oil
accumulation (22.5 BBOE versus 2.9 BBO) and
therefore more likely to be developed (table S1).
The aggregated results suggest there is a high
probability (>95% chance) that more than 770 TCF
of gas occurs north of the Arctic Circle, a one in two
chance (50%) that more than 1547 TCF may be
found, and a 1 in 20 chance (5%) that as much as
2990 TCF could be added to proved reserves from
new discoveries. For comparison, current world gas
consumption is almost 110 TCF per year. The
median estimate of undiscovered gas is a volume
larger than the volume of total gas so far discovered
in the Arctic and represents about 30% of global
undiscovered conventional gas.
Two-thirds of the undiscovered gas is in just four
AUs (Figs. 2 and 4): South Kara Sea (607 TCF),
South Barents Basin (184 TCF), North Barents
Basin (117 TCF), and the Alaska Platform (122
TCF). The South Kara Sea, the offshore part of the
northern West Siberian Basin, contains almost 39%
of the undiscovered gas and is the most prospective
hydrocarbon province in the Arctic. Although
substantial amounts of gas may be found in Alaska,
Canada, and Greenland, the undiscovered gas
resource is concentrated in Russian territory, and
its development would reinforce the preeminent
strategic resource position of that country.
It is important to note that these estimates do not
include technological or economic risks, so a
substantial fraction of the estimated undiscovered
resources might never be produced. Development
will depend on market conditions, technological
innovation, and the sizes of undiscovered accumu-
lations. Moreover, these first estimates are, in many
cases, based on very scant geological information,
and our understanding of Arctic resources will
certainly change as more data become available.
References and Notes
1. IHS Incorporated, International Petroleum Exploration
and Production Database (IHS Incorporated, Englewood,
CO, 2007).
Fig. 3. Estimated undiscovered oil resources, in BBO, north of the Arctic Circle in AUs of the CARA.
Vertical lines indicate the range of estimated oil resources from a 5% probability (fifth fractile) to a 95%
probability (95th fractile). Horizontal lines correspond to mean estimated oil volumes.
Fig. 4. Estimated undiscovered natural gas resources, in TCF, north of the Arctic Circle in AUs of the CARA.
Vertical lines indicate the range of estimated natural gas resources from a 5% probability (fifth fractile) to a
95% probability (95th fractile). Horizontal lines correspond to mean estimated natural gas volumes.
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2. Materials and methods are available as supporting
material on Science Online.
3. A. Grantz, R. A. Scott, S. S. Drachev, T. E. Moore, “Maps
showing the sedimentary successions of the Arctic Region
(58°-64° to 90° N) that may be prospective for
hydrocarbons,”American Association of Petroleum
Geologists GIS-UDRIL Open-File Spatial Library, 2009,
http://gisudril.aapg.org/gisdemo/.
4. U.S. Geological Survey, “Circum-Arctic Resource Appraisal
(north of the Arctic Circle) assessment units GIS data,”
2009, http://energy.usgs.gov/arctic/.
5. USGS World Assessment Team, “U.S. Geological Survey
world petroleum assessment 2000: Description and
results,”USGS Digital Data Series DDS60, 2000,
http://pubs.usgs.gov/dds/dds-060/.
6. R. R. Charpentier, T. R. Klett, E. D. Attanasi, “Database
for assessment of assessment unit-scale analogs
(exclusive of the United States),”U.S. Geological Survey
Open-File Report 2007-1404, 2008, http://pubs.usgs.
gov/of/2007/1404/.
7. R. R. Charpentier, paper presented at the 2008 American
Association of Petroleum Geologists Annual Convention
and Exhibition, San Antonio, TX, 22 April 2008.
8. J. H. Schuenemeyer, “Procedures for aggregation used in
the Circum-Arctic Resource Appraisal,”U.S. Geological
Survey Open File Report, in press.
9. British Petroleum (BP) Public Limited Company, “BP
statistical review of world energy 2008,”London, 2008,
http://www.bp.com/statisticalreview.
10. We thank P.I. McLabe and R.S. Bishop for their comments
on an earlier version of the manuscript.
Supporting Online Material
www.sciencemag.org/cgi/content/full/324/5931/1175/DC1
Materials and Methods
Table S1
8 December 2008; accepted 16 March 2009
10.1126/science.1169467
Volcanism, Mass Extinction, and
Carbon Isotope Fluctuations in the
Middle Permian of China
Paul B. Wignall,
1
*Yadong Sun,
2
David P. G. Bond,
1
Gareth Izon,
3
Robert J. Newton,
1
Stéphanie Védrine,
1
Mike Widdowson,
3
Jason R. Ali,
4
Xulong Lai,
2
Haishui Jiang,
2
Helen Cope,
5
Simon H. Bottrell
1
The 260-million-year-old Emeishan volcanic province of southwest China overlies and is
interbedded with Middle Permian carbonates that contain a record of the Guadalupian mass
extinction. Sections in the region thus provide an opportunity to directly monitor the relative
timing of extinction and volcanism within the same locations. These show that the onset of
volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst
fusulinacean foraminifers and calcareous algae. The temporal coincidence of these two phenomena
supports the idea of a cause-and-effect relationship. The crisis predates the onset of a major
negative carbon isotope excursion that points to subsequent severe disturbance of the
ocean-atmosphere carbon cycle.
The temporal link between mass extinc-
tion events and large igneous province
volcanism is one of the most intriguing
relationships in Earth’s history, with the end-
Permian extinction–Siberian Traps association
being the most celebrated (1,2), but the causal
link is far from resolved. A major problem is
that the site of volcanism can rarely be directly
correlated with the marine extinction record
(3), and so comparison can only be achieved
with the use of geochronological bio- and che-
mostratigraphic correlation techniques, with
their inherent timing inaccuracies. To clarify
some of these relations, we have studied the
Emeishan flood basalt province in southwest
China, where Middle Permian platform lime-
stones pass up into a volcanic pile with inter-
bedded limestones. These record both a marine
extinction record and a major C isotope excur-
sion. Thus, we were able to document multiple
phenomena associated withthe Middle Permian
mass extinction within the same geological
sections.
Middle Permian (Guadalupian) platform
carbonate rocks of the Maokou Formation are
widespread throughout south China. In western
Guizhou, southern Sichuan, and Yunnan Prov-
inces they pass laterally into the flows of the
Emeishan large igneous province (Fig. 1). The
original size of the province is difficult to esti-
mate because much has been eroded (scattered
outcrops of contemporaneous volcanic rocks
are found up to 300 km from the main sections,
Fig. 1), but its main outcrops cover 2.5 × 10
5
km
2
in southwest China; the original volume
was probably substantiallyless than 1 × 10
6
km
3
(4). Despite their relatively small size, the co-
incidental timing of the Emeishan eruptions
with the Guadalupian mass extinction has led to
suggestions that they may be implicated in this
environmental calamity (2,5).
Sections from both within the volcanic prov-
ince and around its margins record a prolonged
phase of stable carbonate platform deposition
before its termination by abrupt base-level
changes. To the north of the province, in north-
ern Sichuan, the Maokou limestones are capped
by a karstic surface dated by conodont studies to
1
School of Earth and Environment, University of Leeds, Leeds
LS2 9JT, UK.
2
Faculty of Earth Sciences, China University of
Geosciences, Wuhan, Hubei 430074, China.
3
Department of
Earth and Environmental Science, The Open University, Milton
Keynes MK7 6AA, UK.
4
Department of Earth Sciences,
Pokfulam Road, University of Hong Kong.
5
Department of
Bioengineering, University of Strathclyde, Wolfson Building,
106 Rottenrow, Glasgow G4 0NW, UK.
*To whom correspondence should be addressed. E-mail:
p.wignall@see.leeds.ac.uk
Fig. 1. Outcrop map (red)
of the Emeishan large igne-
ous province in southwest
China (4).
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