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We evaluated the geochemical transformations that would likely occur after injecting CO2 into a sandstone formation using The Geochemist's Workbench®, with the intent of simulating CO2 solution and mineral storage mechanisms. We used a hypothetical reservoir intended to closely resemble the Lamotte Sandstone in southwest Missouri, a reservoir rock found at about 600-m (1970-ft) depth, well above the recommended depth for CO2 sequestration of 800 m (2625 ft). In the absence of specific water chemistry and lithology data for this formation at the proposed injection site, the model considered two best estimates of each input parameter. Carbon dioxide (CO2) sequestered in the dissolved phase was found to range between 76.74 and 76.80 g/kg free water, and the pH dropped from 7.7 to 4.8 after a 10-yr injection period. During a 50-yr postinjection interval with no additional CO2(g) added, the model predicted the pH to rise from 4.8 to 5.3 and various minerals to precipitate, among them magnesite, nontronite-Mg, and gibbsite, as well as smaller amounts of siderite and dolomite. Magnesite, siderite, and dolomite contribute to removal of carbon. In general, the model is very flexible, allowing the user to incorporate variations in temperature, pressure, water chemistry, solid-phase mineralogy, and kinetics. Modeling steps are described here as well as the results, which are all based in 1 kg of free water. To determine the total sequestration potential, transport modeling is needed, in addition to the geochemical modeling presented here.
Lea Nondorf received her M.S. degree in geospatial sciences from the Missouri State University in 2010. At this time, she is working with the Arkansas Geological Survey in Little Rock, Arkansas, mapping the geology of areas along the Buffalo National River in northern Arkansas as part of a National Park Service grant.
Melida Gutierrez obtained a Ph.D. in geohydrology from the University of Texas at El Paso in 1992. She is currently a professor in geology at Missouri State University, teaching courses in geology and geochemistry. Her research focuses on stream-water quality and rock-water interaction.
Thomas G. Plymate is a professor of geology and head of the Department of Geography, Geology, and Planning at Missouri State University. He received his Ph.D. from the University of Minnesota in 1986. His research interests include optical and x-ray mineralogy and igneous and metamorphic petrology of Proterozoic terranes.