Most energy used to meet human

needs is derived from the combustion of

fossil fuels (natural gas, oil, and coal),

which releases carbon to the atmosphere,

primarily as carbon dioxide (CO2). The

atmospheric concentration of CO2, a

greenhouse gas, is increasing, raising

concerns that solar heat will be trapped

and the average surficial temperature of

the Earth will rise in response. Global

warming studies predict that climate

changes resulting from increases in

atmospheric CO2 will adversely affect

life on Earth.

In the 200 years since the industrial

revolution, the world’s population has

grown from about 800 million to over 6

billion people and the CO2 content of the

atmosphere has risen from about 280 to

about 360 parts per million by volume, a

30 percent increase (fig. 1). International

concern about potential global climate

change has spurred discussions about limiting the amount of CO2 and other greenhouse gases released to the atmosphere.

Although there is no U.S. Government

policy concerning CO2 emissions, multinational corporations will face CO2 regulations in countries that have resolved to

reduce emissions. Furthermore, the Clear

Skies Act of 2003 was introduced in the

U.S. House of Representatives as House

bill HR 999 and the Senate as Senate bill

S. 485 on February 27, 2003. The act proposes a voluntary CO2 emissions reduction

plan (http://www.epa.gov/clearskies/). To

evaluate all options for reducing CO2

emissions, we need to study the potential

of geologic reservoirs and geologic

processes to store CO2 (fig. 2).

The concept of controlling the level

of CO2 in the atmosphere is generally

referred to as “carbon management.”

Carbon management includes the following strategies to reduce carbon emissions:

carbon capture and sequestration,

enhanced efficiency of power use and

generation, the use of low-carbon fuels,

and the use of renewable energy sources.

Geologic Sequestration of Carbon Dioxide—

An Energy Resource Perspective

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sheet FS–026–03

March 2003

Figure 2. Potential CO2 sequestration reservoirs and products.

Red lines indicate CO2 being pumped into the reservoirs for

sequestration, green lines indicate enhanced recovery of fossil

fuels caused by CO2 sequestration, and the blue line indicates

conventional recovery of fossil fuels. The offshore natural gas

production (blue line) and CO2 sequestration scenario is currently occurring off the coast of Norway at the Sleipner complex (fig. 3), operated by Statoil. There, the gas produced is a

mixture of CO2 and methane. The CO2 is removed and injected into a nearby saline aquifer.

-450 -350 -250 -150 -50 50

200

300

400

ATMOSPHERIC CO2 (ppmv)

Human perturbation

THOUSANDS OF YEARS BEFORE PRESENT

Figure 1. Ice cores indicate that in the past

420,000 years, the concentration of CO2 in

the atmosphere has ranged from 180 to 280

parts per million by volume (ppmv).The current

CO2 atmospheric concentration is ~360 ppmv;

this dramatic increase is primarily the result of

human combustion of fossil fuels. Graph is

excerpted with permission from Falkowski and

others (2000); copyright 2000, American Association for the Advancement of Science.

Depleted 

hydrocarbon 

reservoir

Unminable 

coal seam

Reservoir

trap/seal

Deep 

saline 

aquifer

Pipeline transporting 

CO2 from powerplants to 

injection site

Injection of CO2

into geologic 

reservoirs

Natural gas 

reservoir

Saline aquifer

Coal-bedmethane 

production

Offshore natural gas

production with CO2

separation and sequestration
Carbon sequestration, broadly

defined, is a term that includes the

removal of CO2 from the atmosphere by

agricultural modifications and reforestation as well as the reduction of CO2

emissions by capture and storage. Storage

of anthropogenic CO2 within geologic

reservoirs is a method of carbon sequestration. The U.S. Geological Survey

(USGS) is currently studying geologic

options for storing CO2 in depleted oil

and gas reservoirs, unminable coal

seams, or saline aquifers (fig. 2).

USGS Project Activities

USGS project activities focus on

two broad themes. First, research is

being conducted by the USGS on the

geologic and geochemical factors that

control the capacity to store CO2 in geologic formations. The tasks of this part

of the project include the following:

(i) characterizing possible interactions

between the injected CO2 and any of the

components of the reservoirs and (ii)

comparing benefits and risks of various

storage reservoirs. The second topic of

research involves identifying potential

geologic reservoirs and assessing how

much CO2 could be sequestered within

them. One product planned to come

from this assessment is a geographic

information system (GIS) map that will

compare the location of major CO2

sources with the size, location, and

type of potential storage reservoirs.

Understanding the spatial relations

between the CO2 sources and potential

geologic sinks will help to determine

the extent of infrastructure needed to

complete the sequestration project.

These two broad areas of research will

help to assess the scientific and economic feasibility of using CO2 sequestration

in geologic formations as a method to

slow the increase of atmospheric CO2

levels.

In addition to these tasks, the USGS

is collaborating with the National Energy

Technology Laboratory (NETL) of the

U.S. Department of Energy and with the

NETL-supported consortia GEO-SEQ and

MIDCARB. Collaborative USGS activities are focused on new measurements of

the solubility of CO2 in brines and on

methods of assessing the CO2 sequestration capacity of geologic formations.

What We Need to Know

Initial strategies for geologic sequestration of CO2 should focus on the most

cost-effective options. Therefore, these

options need to be identified. Storage sites

that are close to CO2 sources (powerplants)

lead to relatively lower transportation

costs. Furthermore, CO2 sequestration in

some oil, gas, and coal-bed-methane

reservoirs has the potential to increase the

amount of fossil fuel that can be removed

from those reservoirs. These enhanced

recovery methods—for example, enhanced

oil recovery (EOR), enhanced coal-bedmethane recovery, or enhanced gas recovery

(EGR)—have an economic payback that

will help to subsidize the net cost of CO2

storage. Additionally, one of the important

goals of this project is to determine storage capacity of both enhanced recovery

reservoirs and non-economic reservoirs.

Reference Cited

Falkowski, P., Scholes, R.J., Boyle, E.,

Canadell, J., Canfield, D., Elser, J.,

Gruber, N., Hibbard, K., Högberg, P.,

Linder, S., Mackenzie, F.T., Moore,

B., III, Pedersen, T., Rosenthal, Y.,

Seitzinger, S., Smetacek, V., and

Steffen, W., 2000, The global carbon

cycle; A test of our knowledge of

Earth as a system: Science, v. 290,

p. 291–296. (Also available online at

http://gcte.org/Glob-C-cycle.pdf)

For more information, please contact:

Robert C. Burruss

Sean T. Brennan

U.S. Geological Survey

MS 956, National Center

12201 Sunrise Valley Drive

Reston, VA 20192

E-mail: burruss@usgs.gov

sbrennan@usgs.gov

Figure 3. The Sleipner complex off the coast of Norway. Natural gas produced in the Sleipner

field is high in CO 2; this CO2 is removed from the natural gas stream and is then pumped

into the Utsira Formation, which is a highly permeable sandstone. The operator of the Sleipner

field, Statoil, geologically sequesters the CO2 because the sequestration cost is less than the

Norwegian carbon emission tax. Photograph is courtesy of øyvind Hagen, Statoil.