U.S. Geological Survey
Fact Sheet 26-03
March 2003 - Online Version 1.0
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.
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.
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).
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.
Figure 3. The Sleipner complex off the coast of Norway. Natural gas produced in the Sleipner field is high in CO2; 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.
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.
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 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.
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-bed-methane 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.
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
U.S. Department of the Interior, U.S. Geological Survey
For more information, contact Robert C. Burruss or Sean T. Brennan
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