|Pie chart showing mean estimates by the USGS of technically accessible storage resources (TASR) for CO2 by region. Click to enlarge.|
The United States has the potential to store a mean of 3,000 gigatonnes of carbon dioxide in geologic basins throughout the country, according to the first detailed national geologic carbon sequestration assessment released today by the US Geological Survey (USGS). The assessment comes on the heels of a national climate action plan announced by President Obama. (Earlier post.)
The US Energy Information Administration (EIA) estimates that in 2011, the United States emitted 5.5 metric gigatons of energy-related CO2, while the global emissions of energy-related CO2 totaled 31.6 metric gigatons.
|Carbon sequestration in the President’s climate plan|
|In the climate action plan rolled out by the President earlier this week, carbon sequestration appears in several places:|
|As part of a coming, up to $8-billion DOE solicitation for advanced fossil energy projects;|
|In reference to the US’ role in the Carbon Sequestration Leadership Forum, which engages 23 other countries and economies on carbon capture and sequestration technologies, especially related to coal; and|
|As an acceptable condition for US government support for public financing of new coal plants overseas.|
Based on present-day geologic and hydrologic knowledge of the subsurface and current engineering practices, this assessment looked at the potential for CO2 storage in 36 basins in the United States. The largest potential by far is in the Coastal Plains region, which accounts for 2,000 metric gigatons, or 65%, of the storage potential. Two other regions with significant storage capacity include the Alaska region and the Rocky Mountains and Northern Great Plains region.
Technically accessible storage resources are those that can be accessed using today’s technology and pressurization and injection techniques. The most common method of geologic carbon storage involves pressurizing CO2 gas into a liquid, and then injecting it into subsurface rock layers for long-term storage.
This assessment goes further than all previous assessments in considering the viability of sequestration. For example, all areas with groundwater sources that are considered freshwater by U.S. Environmental Protection Agency (EPA) standards were eliminated from consideration for carbon storage resource potential in this assessment. In addition, the rock layers included in the assessment were limited to those determined to have sufficient natural seals to prevent CO2 from escaping. This assessment also focused only on rock layers located at depths at which CO2 would stay under sufficient pressure to remain liquid.
The study did not evaluate economic viability or accessibility due to land-management or regulatory restrictions for geologic carbon sequestration within these basins.
The assessment is also the first geologically based and probabilistic assessment, estimating a range of 2,400 to 3,700 gigatonnes of CO2 storage potential across the United States.
Although the scope of sequestration included in this assessment is unprecedented, injecting CO2 into geologic formations is not a new process or technology. Carbon dioxide injection has been one method of enhanced oil recovery since the 1980s. The process works by flooding the oil reservoir with liquid CO2, which reduces the viscosity of the hydrocarbons and allows them to flow to the well more easily.
The USGS project results announced today represent an assessment of storage capacity on a regional and national basis, and results are not intended for use in the evaluation of specific sites for potential CO2 storage.
All sedimentary basins in the United States were evaluated, but 36 were assessed because existing geologic conditions or the available data suggested only these 36 met the assessment’s minimum criteria.
The geologic foundation that underpins the assessment was facilitated by data provided by the US EPA, the US Department of Energy, and State geological surveys. The methodology for the assessment released today was developed by the USGS and consistently applied across all 36 basins, so that results are comparable. This national assessment complements the regional estimates that the Department of Energy includes in their periodically updated Atlas.