evaluates opportunities for capture, and considers how the CO₂ might be transported at the scale required.

Figure 7.14 shows estimated cost as a function of the total quantity of CO₂ that could be captured and stored with current technologies at existing U.S. CO₂ sources. It indicates that if all the CO₂ emitted from stationary sources that could be stored at costs below about $50 per tonne were captured, the total emissions reduction would be about 1.5 billion tonnes CO₂, or about 20 percent of current emissions (Dooley et al., 2006). The storage cost shown as negative in Figure 7.14 stems from the use of CO₂ for EOR, which may make use of sources of CO₂ other than power plants (ammonia plants or natural gas purification, for example) in which CO₂ is already separated. About 28 million tonnes CO₂ per year is presently injected for EOR in oil fields in west Texas, though most of that CO₂ comes from natural underground sources.

Significant growth in the amount of CO₂ captured from anthropogenic sources would likely be put to use for EOR in regions where oil fields are within reasonable distance from a source. The existence of a CO₂ price would favor expansion of EOR in such locations as the magnitude of present EOR operations is constrained by the availability of CO₂ for injection. Thus combined EOR and CO₂ storage has the potential to lead to a significant expansion of EOR production from the 200,000 barrels per day produced now.

Long-term geologic storage of carbon dioxide appears to be technologically feasible, but it has yet to be demonstrated at the scale of a large power plant in a variety of geologic repositories.

A suite of projects can be designed to clarify the costs, risks, and environmental impacts of carbon storage. This would enable a determination of whether such plants can become significant contributors to the U.S. power system in a carbon-constrained world. Successful demonstration will require projects spanning the many types of coal, using several capture strategies, at a variety of storage sites, at both power and synfuel plants, and with storage both in deep saline aquifers and in hydrocarbon-bearing seams.