Volume of organic-rich Devonian shale in the Appalachian Basin: relating "black" to organic-matter content: Geologic notes

Some estimates of natural-gas resources in the Devonian shale of the Appalachian basin depend on the volume of organic-rich shale in the basin. A map by L. G. Wallace and W. de Witt showing the thickness and extent of Devonian "black" shale facies in the Appalachian basin is widely used as an indicator of organic-rich shale, but the map is derived from subjective evaluations of shale color. Wallace and de Witt's definition of "black" is shown here to correspond to an organic-matter content of approximately 4% or more by volume and a Munsell color value for dry pressed-powder samples of about N5 (medium gray) or darker. The volume of Devonian shale with an organic-matter content greater than 2.0% by volume (a definition of "organic-rich" that is preferred by the writers) a erages 1.44 times that of the "black" shale of Wallace and de Witt, and totals about 2,574 × 10¹² cu ft (72.9 × 10¹² cu m) in the Appalachian basin.