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Staff Accomplishments

Greenhouse Gas: Caught Between a Rock and a Hard Place

July 2007
Results: Findings from recent laboratory experiments confirm carbon dioxide injected into deeply buried basalt formations can be effectively trapped by the relatively rapid formation of stable carbonate mineral compounds. A key discovery by researchers at the Pacific Northwest National Laboratory is that these carbonate minerals form in a relatively short period of time after carbon dioxide injection, which should enhance long-term retention. These results verify their hypothesis that in situ mineralization rates are quite promising and that field testing of carbon dioxide storage in these formations should be accelerated. Why it matters: Given the central role played by fossil fuels in the global economy, a great deal of current research and development is focused on creating the means to reduce carbon dioxide emissions cost effectively. Carbon dioxide capture and storage represents a set of technologies aimed at capturing carbon dioxide from large, stationary sources such as industrial and power generation facilities, and injecting the compressed carbon dioxide into deeply buried geologic formations to permanently isolate it from the atmosphere. This class of technologies appears to hold significant promise through its ability to cost effectively reduce hundreds of billions of tons of carbon dioxide emissions from large, industrial sources if society can address the technological and policy issues that currently stand in the way of large-scale deployment of CCS. Researchers at PNNL have shown that flood basalts have significant potential capacity for safely isolating vast quantities of anthropogenic carbon dioxide in the United States and abroad in key developing nations such as India. Basalt flows have many geologic characteristics that make them attractive candidates for carbon dioxide storage. These formations contain regions that are porous and permeable, qualities that make the rocks capable of storing carbon dioxide. Just above these porous, permeable layers lie low-permeability layers of rock from subsequent flows that should act as an effective seal to trap the carbon dioxide in the deep subsurface allowing time for mineralization reactions to occur. If this approach proves viable, major flood basalts in the United States and India would provide significant carbon dioxide storage capacity, as well as geologic storage options for certain regions where more conventional storage options, like depleted oil and gas fields, are limited. Methods: Computing the rate of carbonate mineral formation in a real basalt formation requires, at a minimum, detailed information about three primary characteristics of the formation:
  1. solution concentrations of calcium, magnesium, iron, and manganese required to precipitate calcite or other carbonates
  2. release rate of these elements from the basalt
  3. concentration of carbon dioxide dissolved in the formation waters.
Because all three characteristics are strongly coupled, rigorous calculation of carbonate mineralization rates requires solving a complex reactive chemical transport problem. In this study, the research team used empirical measurements to understand the rate at which carbonate minerals can form in the basalt, permanently storing the carbon dioxide. Next steps: The research team is currently performing more complex calculations to obtain more detailed results. Additional work is needed to better understand the kinetics of these mineralization reactions as a function of temperature, carbon dioxide pressure, basalt composition, and especially the dispersion of carbon dioxide within and around basalts on a large scale. Acknowledgments: The research team included Pete McGrail, Todd Schaef, Yi-Ju Chien, James Dooley, Casie Davidson, all Pacific Northwest National Laboratory; and Anita Ho, Flathead Valley Community College in Kalispell, Montana. This research was supported by Laboratory Directed Research and Development funding and by the U.S. Department of Energy, Office of Fossil Energy. References: McGrail BP, HT Schaef, AM Ho, Y Chien, JJ Dooley, and CL Davidson. 2006. "Potential for Carbon Dioxide Sequestration in Flood Basalts." Journal of Geophysical Research. Solid Earth 111(B12) Art. No. B12201, doi:10.1029/2005JB004169.

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