Depositional and diagenetic variability within the Cambrian Mount Simon Sandstone: Implications for carbon dioxide sequestration Brenda B. Bowen, Raul I. Ochoa, Nathan D. Wilkens, James Brophy, Thomas R. Lovell, Nick Fischietto, Cristian R. Medina, and John A. Rupp ABSTRACT The Cambrian Mount Simon Sandstone is the major target reservoir for ongoing geologic carbon dioxide (CO 2 ) sequestration demon- strations throughout the midwest United States. The potential CO 2 reservoir capacity, reactivity, and ultimate fate of injected CO 2 depend on textural and compositional properties determined by depositional and diagenetic histories that vary vertically and lat- erally across the formation. Effective and efficient prediction and use of the available pore space requires detailed knowledge of the depositional and diagenetic textures and mineralogy, how these variables control the petrophysical character of the reservoir, and how they vary spatially. Here, we summarize the reservoir charac- teristics of the Mount Simon Sandstone based on examination of geophysical logs, cores, cuttings, and analysis of more than 150 thin sections. These samples represent different parts of the formation and depth ranges of more than 9000 ft (>2743 m) across the Illinois Basin and surrounding areas. This work demonstrates that overall reservoir quality and, specifically, porosity do not exhibit a simple relationship with depth, but vary both laterally and with depth be- cause of changes in the primary depositional facies, framework com- position (i.e., feldspar concentration), and diverse diagenetic modifications. Diagenetic processes that have been significant in modifying the reservoir include formation of iron oxide grain coat- ings, chemical compaction, feldspar precipitation and dissolution, multiple generations of quartz overgrowth cementation, clay miner- al precipitation, and iron oxide cementation. These variables pro- vide important inputs for calculating CO 2 capacity potential, AUTHORS Brenda B. Bowen  Purdue University, West Lafayette, Indiana 47907; bbowen@purdue.edu Brenda B. Bowen is an assistant professor in the Department of Earth and Atmospheric Sciences at Purdue University. She received her B.S. and M.S. degrees in earth science from the University of California, Santa Cruz, and her Ph.D. in geology from the University of Utah in 2005. Her research is focused on understanding depositional and diagenetic processes that influence reservoir char- acteristics and paleoenvironmental records. Raul I. Ochoa  Purdue University, West Lafayette, Indiana 47907 Raul I. Ochoa is an M.S. student at Purdue Uni- versity, studying reservoir characterization and diagenetic analysis of the Mount Simon Sandstone in the Illinois Basin related to geologic CO 2 se- questration. He received his B.S. degree from the University of Texas at El Paso in geology in 2008. Nathan D. Wilkens  Purdue University, West Lafayette, Indiana 47907 Nathan D. Wilkens is a postdoctoral research as- sociate in the Department of Earth and Atmo- spheric Sciences at Purdue University. He earned his B.S. degree in geology in 2003 and a Ph.D. in geological sciences from Arizona State Univer- sity in 2008. His research emphasis has been on depositional environments and paleoecology of terrestrial environments. James Brophy  Indiana University, Bloomington, Indiana 47405 James Brophy is an associate professor of igneous petrology at Indiana University. His research spe- cializes in the origin and differentiation of magma and uses a combination of field, analytical, theo- retical, and experimental approaches. An important component of his work is the characterization of rock texture, mineralogy, and mineral composition through the application of petrographic and elec- tron microprobe analytical techniques. Thomas R. Lovell  Purdue University, West Lafayette, Indiana 47907 Thomas R. Lovell is a Ph.D. student at Purdue Uni- versity, studying interactions between provenance and overall reservoir development in the Mount Simon Sandstone. He completed his M.S. thesis research at the University of Alabama while study- ing detrital zircon geochronology of an Early Ju- rassic reservoir in the Gulf of Mexico and his B.S. degree at the University of Tennessee-Chattanooga. Copyright ©2011. The American Association of Petroleum Geologists/Division of Environmental Geosciences. All rights reserved. DOI:10.1306/eg.07271010012 Environmental Geosciences, v. 18, no. 2 (June 2011), pp. 69 – 89 69