CO₂ Sequestration in Gas Shales of Kentucky

Nuttall, Brandon C. ¹, Drahovzal, James A. ¹, Eble, Cortland F. ¹, and Bustin, R. Marc ²

¹Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky

²Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, Canada

Continued economic growth will depend on the availability of reliable energy. Improved efficiency and alternate energy sources will reduce total CO₂ emissions, but carbon capture and storage are required to meet goals of stabilizing CO₂ in the atmosphere. Continuous, low-permeability, fractured, organic-rich gas shales are a possible sequestration target.. Devonian shales underlie approximately two-thirds of Kentucky. These shales are the source and trap for large quantities of natural gas. Enhanced natural gas recovery may be possible as stored CO₂ displaces methane.

Drill cuttings and cores from Kentucky, West Virginia, and Indiana were sampled, and adsorption isotherms collected. Sidewall core samples were analyzed for their potential CO₂ uptake and resulting methane displacement. Digital well logs were used to model TOC and CO₂ adsorption capacity. Average random vitrinite reflectance data range from 0.78 to 1.59, the upper oil to wet gas and condensate maturity range. TOC ranges from 0.69 to 4.62 percent. CO₂ adsorption capacity at 400 psi ranges from 19 to 86 standard cubic feet per ton of shale.

Initial estimates based on these data indicate a sequestration capacity of as much as 28 billion tons in the deeper and thicker parts of the Devonian shales in Kentucky. New estimates based on adsorption and geophysical log data are being compiled. Should shales prove to be a viable geologic sink for CO₂, their extensive occurrence in Paleozoic basins across North America would make them an attractive regional target for economic CO₂ storage and enhanced natural gas production.