Carbon Dioxide, the Main Greenhouse Effect Gas, Could Be Stored in Black Shale Deposits

Scientists are concerned about the ever increasing amount of greenhouse effect carbon dioxide gas (CO2) into the atmosphere and look for possible technologies to manage CO2.

Geologist Brandon Nuttall at the Kentucky Geological Survey (KGS) at the University of Kentucky, has seen the option for geologic sequestration of captured CO2 in Devonian black shales, organic-rich rocks found in the geological profile of more than half of Kentucky. The carbon dioxide for underground storage derives from coal burning, cement plants, and different other types of plants.

The shale deposits are generally thought to be the top of much bigger deeper storage reservoirs that would prevent sequestered CO2 from escaping back to the atmosphere. Filling in the black shales with CO2 will force the natural gas from the interior structure of the rocks to come out and to be recoverable.

Nuttall determined during a three years study that the deeper and thicker parts of the Devonian shales in Kentucky could provide a potentially large geologic storage reservoir for captured CO2. The large area of expansion of black shales deposits across North America could make them an suitable storage warehouse for CO2.

Analysis of black shale samples achieved from drilled wells in the Appalachian Basin of eastern Kentucky and the Illinois Basin in Indiana demonstrated that rocks could incorporate as much as 28 billion tons of CO2 only in Kentucky, from which 6.2 billion tons in the Big Sandy Gas Field area of eastern Kentucky alone. "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."

Nuttall's efforts to demonstrate the economic viability of natural gas production through CO2 injection inside black shales will lead to an increased knowledge of these rocks as gas reservoirs, possible storage deposits and, of course, of the real size of these layers.