As concern has grown over the effects of the human release of carbon dioxide (CO2) gas into the atmosphere, so too has research into technologies to manage CO2. One such research project, overseen by geologist Brandon Nuttall at the Kentucky Geological Survey (KGS) at the University of Kentucky, has investigated the option for geologic sequestration of captured CO2 in Devonian black shales, organic-rich rocks found beneath about two thirds of Kentucky.
Geologic sequestration refers to the process of permanent underground storage of carbon dioxide captured from sources such as coal-fired power plants, cement plants, and others manufacturing plants. Widespread deposits of shale are generally thought to be the seal or cap for deeper storage reservoirs that would prevent sequestered CO2 from leaking to the surface. Injection of CO2 into black gas-producing shales may have an additional value of enhancing the recovery of natural gas.
In the three year project funded by National Energy Technology Laboratory of the U.S. Department of Energy, Nuttall determined that the deeper and thicker parts of the Devonian shales in Kentucky could provide a potentially large geologic storage reservoir for captured CO2. In fact, the extensive occurrence of shales in geologic basins across North America would make them an attractive regional reservoir for economic CO2 sequestration.
Analysis of 43 shale samples from 11 recent drilled wells in the Appalachian Basin of eastern Kentucky and the Illinois Basin in Indiana demonstrated that Devonian black shales in Kentucky could sequester as much as 28 billion tons of injected CO2. The analyses done for Nuttall’s project indicate that in the five-county Big Sandy Gas Field area of eastern Kentucky alone, 6.2 billion tons of CO2 could be sequestered.
“In the sequestration process, carbon dioxide is ‘adsorbed’ by the shales, which means the CO2 forms a molecular bond with the shale,” Nuttall says. “The shale may, in turn, ‘desorb’ natural gas when carbon dioxide is present. Natural gas fields in shaly areas are therefore considered potential candidate sites for carbon sequestration because the injection of CO2 for permanent storage may also help extract additional natural gas.”
The project’s final report, entitled “Analysis of the Devonian Black Shale in Kentucky for Potential Carbon Dioxide Sequestration and Enhanced Natural Gas Production,” is available online at the KGS web site. See http://www.uky.edu/KGS/emsweb/devsh/devshseq.html.
Nuttall’s Devonian shale research is continuing, in an effort to demonstrate the economic viability of the production of natural gas displaced by CO2 injection. He is working with several surrounding states on research efforts funded by the Department of Energy’s Regional Carbon Sequestration Partnerships programs, which are active nationwide. These efforts will result in a better understanding of shales as gas reservoirs, sequestration targets, and seals for deeper reservoirs.
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