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Abstract

Nutall, B. C., J. A. Drahovzal, C. F. Eble, and R. M. Bustin, 2009, Regional assessment of suitability of organic-rich gas shales for carbon sequestration: An example from the Devonian shales of the Illinois and Appalachian Basins, Kentucky, in M. Grobe, J. C. Pashin, and R. L. Dodge, eds., Carbon dioxide sequestration in geological media—State of the science: AAPG Studies in Geology 59, p. 173–190.

DOI:10.1306/13171239St593381

Copyright copy2009 by The American Association of Petroleum Geologists.

Regional Assessment of Suitability of Organic-Rich Gas Shales for Carbon Sequestration: An Example from the Devonian Shales of the Illinois and Appalachian Basins, Kentucky

Brandon C. Nuttall,1 James A. Drahovzal,2 Cortland F. Eble,3 R. Marc Bustin4

1Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky, U.S.A.
2Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky, U.S.A.
3Kentucky Geological Survey, University of Kentucky, Lexington, Kentucky, U.S.A.
4Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia, Canada

ACKNOWLEDGMENTS

We would like to thank the University of Kentucky Research Foundation and the Office of Sponsored Projects Administration for their assistance and support. Ed Rothman of Columbia Natural Resources and Jay Terry of Schlumberger were instrumental in providing access to a drill hole and obtaining advanced well logs. Joe Meglen of Interstate Natural Gas, Pikeville, Kentucky, contributed the ECS log and analysis for Interstate's well in Martin County and provided access to obtain additional sidewall cores. John Rupp of the Indiana Geological Survey provided core samples of the New Albany Shale and accompanying data. Henry Francis, Sue Rimmer, Frank Ettensohn, Bob Cluff, Jackie Silvers, Margaret L. Smath, and Leah Barth all contributed to the success of this research. This study was sponsored by an agency of the United States Government under contract DE-FC26-02NT41442. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service mark by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The view and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

ABSTRACT

In gas shales, natural gas occurs both as free gas in intergranular and fracture porosity and as an adsorbed phase onto the surfaces of clays and organic matter, analogous to natural gas storage in coalbeds. The adsorption capacity of shales from Kentucky, Indiana, and West Virginia was estimated using drill cuttings and sidewall cores to determine both CO2 and CH4 adsorption isotherms. Elemental capture spectroscopy logs were analyzed to investigate possible correlations between adsorption capacity and mineralogy.

The maturity of the shale was characterized using average random vitrinite reflectance data yielding values ranging from 0.78 to 1.59 (upper oil to wet gas and condensate hydrocarbon maturity values). Total organic carbon (TOC) content ranges from 0.69 to 14%. Calculated CO2 adsorption capacities at 2.75 MPa range from a low of 0.4 m3/t (14.1 ft3/t) to more than 4.2 m3/t (148.3 ft3/t). A direct linear correlation between measured TOC and the adsorption capacity of the shale has been determined; CO2 adsorption capacity increases with increasing TOC. Data also suggest that CO2 is preferentially adsorbed (5.3:1) and would displace CH4, leading to a potential method for enhancing natural gas recovery in gas shales.

Initial estimates of the volume of CO2 sequesterable in the shale based on these data indicate a capacity of as much as 25 billion t in the deeper and thicker parts of the Devonian shales across Kentucky. Discounting the uncertainties in reservoir volume and injection efficiency, these results indicate that gas shales could provide a potentially large geologic sink for CO2. Moreover, the extensive occurrence of gas shales in Paleozoic and Mesozoic basins across North America makes them an attractive regional target for economic CO2 storage and enhanced natural gas production.

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