Preliminary Characterization of Visual Kerogen Types, Thermal Maturity, Total Organic Carbon, and Oil Yield Potential of Devonian Shale in the Appalachian and Illinois Basins

Sandra G. Neuzil, Joseph A. East, Christopher S. Swezey, and Frank T. Dulong
U.S. Geological Survey, Reston, VA 20192 USA, [email protected]

U.S. Department of Energy, Eastern Gas Shale Program (EGSP) Monsanto data (published 1977-1981) allow comparison of visual kerogen types, thermal maturity indices (vitrinite reflectance, Ro), total organic carbon (TOC), and oil yield potential (Fischer assay) in Devonian shale from the Appalachian and Illinois Basins. In the Appalachian Basin, visual kerogen types are predominantly terrestrial, herbaceous and woody-coaly. Ro values (n=586) range from 0.26 to 2.69%. TOC values (n=1030) range from 0.05 to 13% (geometric mean: 0.92%). The Marcellus Shale and Ohio Shale have greater TOC values (geometric means: 3.1% and 1.5%, respectively) than other Devonian shales in the basin. Most oil yield values are from the Ohio Shale (n=66), with a range from 0.5 to 33 liters/metric ton (l/t) and geometric mean of 3.8 l/t. In the Illinois Basin, visual kerogen types are predominantly herbaceous with secondary amorphous-algal components. Ro values (n=54) range from 0.33 to 1.60%. TOC values (n=83) range from 0.14 to 14% (geometric mean: 1.9%). In the New Albany Group, the Grassy Creek Shale has greater TOC values than the Selmier Shale (geometric means: 3.0 and 1.4%, respectively). Most oil yield values are from the Grassy Creek Shale (n=21), with a range from 1.0 to 60 l/t (geometric mean: 18 l/t). For both basins, estimates of oil yield are positively correlated with TOC values. Although hydroretorting methods may increase the Fischer assay oil yield by a factor of 2.5, EGSP data suggest that few Devonian shale samples from these basins have sufficient oil yield potential (>40l/t) to be viable oil-shale resources.

AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009