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Carbon Capture and Sequestration (CCS) and Underground Capacity

How much land area does CCS require? It depends on the site.

[!]Note:[/!!] This version contains a correction to the United States' current annual emissions.

Earlier this week, the Guardian highlighted research that questioned the feasibility of carbon capture and sequestration (CCS), the process of trapping carbon dioxide from power plants and storing it underground. Researchers from the University of Houston have claimed that we would need the underground capacity the size of a small state in order to store the CO2 from just one power plant. Geologists and engineers quickly refuted this claim, pointing to the success of ongoing pilot projects.

This latest dispute about CCS raises the question: how do we know if there is room to store CO2 underground?

U.S. Estimates of CO2 Storage Capacity

CCS depends on storing CO2 in deep geological formations underground. But of course, geology varies greatly by region, and some areas are more suitable than others. For example, Texas and Louisiana have the highest potential, while states like Maine, Vermont, and Wisconsin have no storage potential at all.

The US Department of Energy publishes a national atlas of storage capacity by state. The calculations assume that even in areas that look promising for CO2 storage, only 1-4% of available geologic capacity will actually be used for CCS. Even with this limitation, the DOE still estimates overall potential for storage in the US to be at 3,600 to 12,900 billion metric tons of CO2. To put that in perspective, the United States’ current annual CO2 emissions are about 5,814 million metric tons per year. That is why, despite the challenges, CCS is such a potentially important opportunity in the fight against climate change.

CCS and Land Area

When evaluating how much land would be needed to store carbon dioxide, it is important to remember that not all land is created equal in terms of CCS potential. This makes generalizing about CCS an imprecise art. For example, the study cited by the Guardian suggests that a single 500 MW power plant capturing and storing CO2 for 30 years would require 686 mi2 of underground land area, quite a large number. However, the researchers base their calculations on the assumption that the underground geologic reservoir would be only 200 ft thick. If you apply the same methodology to sites with much thicker reservoirs, those power plants would require considerably less land area. That’s why true capacity can only be estimated with site-specific geological information.

Moving Forward with Carbon Capture and Sequestration

CCS for power plants is, to be sure, a complicated process. In the United States there is currently one coal fired power plant that is capturing CO2, injecting it and storing it underground today (the Mountaineer Project in New Haven, West Virginia). Others are in the planning stages, and there are many legitimate issues that each CCS project will need to address in order to be successful. That’s why the World Resources Institute convened over 90 leaders from national laboratories, research institutes, environmental organizations and energy companies to create guidelines for safe, effective carbon dioxide storage in the United States. These guidelines answer many of the concerns that CCS skeptics have about issues such as seismic events, potential leaks, and correctly evaluating underground capacity.

The important point to remember in discussions about CCS is that every geologic reservoir, and thus every CCS site, is unique. The only way to answer remaining uncertainties about CCS, and bring the cost down over time, is through demonstrations and commercial deployments – in other words, real life, site-specific scenarios – as soon as possible.

Additional Information

Birkholzer, J.T., Zhou, Q., Tsang, C.F., 2009. Large-scale impact of CO2 storage in deep saline aquifers: a sensitivity study on the pressure response in stratified systems. Int. J. Greenhouse Gas Control 3(2), 181–194.

Birkholzer, J.T., Zhou, Q., 2009. Basin-Scale Hydrogeologic Impacts of CO2 Storage: Capacity and Regulatory Implications, International Journal of Greenhouse Gas Control, published online on 8/8/2009, DOI: 10.1016/j.ijggc.2009.07.002.

Dooley, J., Davidson, C., 2010. A Brief Technical Critique of Ehlig- Economides and Economides 2010: “Sequestering Carbon Dioxide in a Closed Underground Volume.” United States Department of Energy. Available here.

Nicot, J.P., 2008. Evaluation of large-scale carbon storage on fresh-water section of aquifers: A Texas study. Int. J. Greenhouse Gas Control 2(4), 582–593.

Yamamoto, H., Zhang, K., Karasaki, K., Marui, A., Uehara, H., Nishikawa, N., 2009. Numerical investigation concerning the impact of CO2 geologic storage on regional groundwater flow. Int. J. Greenhouse Gas Control, 3(5), 586-599.

Zero Emissions Platform, The Realities of Storing Carbon Dioxide

Zhou, Q., Birkholzer, J.T., Tsang, C.F., Rutqvist, J., 2008. A method for quick assessment of CO2 storage capacity in closed and semi-closed saline formations. Int. J. Greenhouse Gas Control 2(4), 626–639.

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