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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.