U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3122

March 2011

The Concept of Geologic Carbon Sequestration

Geologic carbon sequestration is a method of securing 

carbon dioxide (CO2) in deep geologic formations to prevent its 

release to the atmosphere and contribution to global warming 

as a greenhouse gas. The figure illustrates some of the major 

concepts associated with geologic carbon sequestration. The 

figure is not to scale.

Earth’s carbon cycle is the movement of carbon through 

the planet’s atmospheric, biologic, geologic, and hydrologic 

systems (Sundquist and others, 2008). As illustrated in the 

figure, many activities of modern human life have altered the 

carbon cycle by increasing the amount of CO2 produced. For 

example, power generating facilities, petrochemical plants, 

cement production plants, cars and trucks, industrial processes, 

and agricultural practices all produce CO2 and release it into 

the environment. Some of this CO2 is sequestered naturally in 

oceans, plants, and soils, but an increasing amount is making 

its way into the atmosphere. Additional forms of carbon 

sequestration are desirable to offset these increasing emissions.

Carbon dioxide can be captured from stationary sources, 

such as powerplants and other large industrial facilities, 

compressed to a fluid state, and injected deep underground 

into permeable and porous geologic strata in which it will 

remain isolated for long periods of time. This process reduces 

or eliminates the emission of CO2 into the atmosphere. The 

geologic formation in which the gas is stored must be overlain 

by another layer of impermeable rock to seal in the injected 

CO2. In the figure, injection wells are depicted as columns of 

brown “bubbles” with arrows pointed downward into the earth. 

Brown bubbles in the storage formation represent geologic 

storage of CO2.

The technology for sequestering CO2 is still being 

developed, although a few industrial-sized carbon sequestration 

projects are operating worldwide. Several are associated with 

offshore natural gas production, as depicted by the offshore 

platform at the far right of the figure. In addition, for many 

decades CO2 has been injected into geologic formations to boost 

production from oilfields by displacing trapped oil and gas. 

This process, known as enhanced oil recovery, has not been 

optimized for storage of CO2, although significant experience 

has been gained in handling carbon dioxide, including how to 

ship it through pipelines, how to prevent leakage by plugging 

abandoned wells, and how to construct injection wells and 

inject CO2 into them.

Determining the amount of CO2 that can be sequestered 

nationally is important so that long-term plans can be made to 

capture and store CO2. Toward this end, the U.S. Geological 

Survey (USGS) has developed a method for assessing the 

amount of CO2 that might be sequestered in geologic formations 

(Brennan and others, 2010). As illustrated in the figure, the 

method developed by the USGS considers two main types 

of trapping to determine the technically accessible storage 

resource—that is, the amount of CO2 that can be stored using 

current technology. One type, known as buoyant trapping, fills 

the pore space in the rock with CO2; the CO2 is held in place 

by seal formations on the top and sides of the porous rock. This 

type of trapping is somewhat analogous to how oil and gas are 

trapped and is illustrated in the figure by the accumulation of 

CO2 in arc-shaped structures (anticlines) that are overlain by 

low-permeability seal formations that prevent upward leakage. 

The other type of trapping, known as residual trapping, occurs 

as injected CO2 passes through the storage formation and leaves 

some CO2 behind; the CO2 is held in place by surface tension 

in pore spaces. This type of trapping retains less CO2 per given 

rock volume, but there is much more rock for which this type of 

trapping applies.

References Cited

Brennan, S.T., Burruss, R.C., Merrill, M.D., Freeman, 

P.A., and Ruppert, L.F., 2010, A probabilistic assessment 

methodology for the evaluation of geologic carbon 

dioxide storage: U.S. Geological Survey Open-File Report 

2010–1127, 31 p., available only at http://pubs.usgs.gov/

of/2010/1127/.

Sundquist, Eric, Burruss, Robert, Faulkner, Stephen, Gleason, 

Robert, Harden, Jennifer, Kharaka, Yousif, Tieszen, Larry, 

and Waldrop, Mark, 2008, Carbon sequestration to mitigate 

climate change: U.S. Geological Survey Fact Sheet 2008–

3097, 4 p., available at http://pubs.usgs.gov/fs/2008/3097/.

By Douglas W. Duncan and Eric A. Morrissey

For More Information

U.S. Geological Survey

Energy Resources Program

12201 Sunrise Valley Drive, MS 915A

Reston, VA 20192

Internet: http://energy.usgs.gov/
Figure 1. Figure illustrating the concept of geologic carbon sequestration. Figure composed by Douglas W. Duncan and illustrated by Eric A. Morrissey

NOT TO SCALE 

Seal formation

EXPLANATION

CO2 flow

CO2 storage volume Gas flow

Storage formation

Gas

Oil and gas flow Oil

Fault—Arrow indicates relative movement