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Geochemistry of CO₂ sequestration in the Jurassic Navajo Sandstone, Colorado Plateau, Utah

¹ Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112-0111; wparry{at}comcast.net
² Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112-0111; forster{at}arch.utah.edu
³ Department of Geology, Utah State University, Logan, Utah 84322-4505; JPEVANS{at}cc.usu.edu
⁴ Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112-0111; present address: Department of Earth and Atmospheric Science, Purdue University, 550 Stadium Mall Drive, West Lafayette, Indiana 47907; bbowen{at}purdue.edu
⁵ Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, 84112-0111; machan{at}mines.utah.edu

W. T. Parry is professor emeritus of geology and geophysics at the University of Utah. His former positions include associate professor of geoscience at Texas Tech University, Lubbock, Texas, and exploitation engineer for Shell Oil Company, Midland, Texas. He received his B.S. and M.S. degrees and his Ph.D. in geological engineering from the University of Utah, where he taught geology and engineering. His research interests are geochemistry and mineralogy related to ore deposits and faults.

Craig Forster holds degrees in geology (his B.Sc. degree and his Ph.D. from the University of British Columbia and his M.Sc. degree from the University of Waterloo). Throughout the past 30 years, he has been using laboratory, field, and numerical simulation methods to assess fluid-solute-heat flow in fractured geologic systems. He is a research associate professor at the University of Utah and Utah State University.

J. P. Evans is a professor of geology at Utah State University. He was educated at the University of Michigan (B.S. degree in geology and B.S. degree in engineering), and Texas A&M University (M.S. degree and Ph.D. in geology).

Brenda Beitler Bowen is a postdoctoral researcher at Central Michigan University studying fluid-sediment interactions in acid saline systems. She will begin as assistant professor of earth sciences at Purdue University in Fall 2007. She earned her B.S. and M.S. degrees at the University of California, Santa Cruz, and her Ph.D. at the University of Utah studying the diagenesis of the Navajo Sandstone.

Marjorie A. Chan is a professor of geology and department chair at the University of Utah. She received her B.S. degree from the University of California, Davis, and her Ph.D. from the University of Wisconsin, Madison. Her recent and current research focuses on Mesozoic sedimentology and stratigraphy on the Colorado Plateau, with applications to eolian reservoirs and terrestrial iron oxide concretion analogs to Mars.

The Jurassic Navajo Sandstone on the Colorado Plateau of Utah may be considered for sequestration of CO₂, because it is thick, widely distributed, has a high porosity and permeability, is typically horizontal to gently folded, is favorably located with respect to seal strata, and underlies many large point sources of CO₂. However, faulting common on the Colorado Plateau may provide pathways for leakage of the CO₂ similar to present-day geysers and CO₂-charged springs. Natural groundwater present in the Navajo Sandstone includes a range of low-salinity, moderate-salinity with high bicarbonate, and high-salinity waters. Higher salinity waters may have moved from deeper strata under artesian pressures or originated from solution of evaporite in pre-Jurassic rocks. These characteristics make the Navajo Sandstone an excellent analog for examining the geochemistry of CO₂ injection into deep saline aquifers. The storativity of CO₂ in solution is a function of the solubility of CO₂ in these waters, which is dependent on salinity, temperature, and pressure. Geochemical modeling shows that the coolest, least saline water can contain the most CO₂ in solution. Dissolving CO₂ in the water lowers the pH, so that no minerals precipitate, and the Navajo Sandstone contains only small amounts of mineral that may consume the H⁺. The reaction of the acidic water produced by dissolving CO₂ with K-feldspar and minor clays and calcite in the sandstone throughout 500 yr consumes little H⁺ and produces only small amounts of product minerals. The Navajo Sandstone likely would not store significant CO₂ as mineral precipitate, and thus, stored volumes of CO₂ would be limited by its solubility in the in-situ water and storage as free CO₂ in pore space.