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Cambrian Rogersville Shale: A Potential New Unconventional Reservoir in the Southern Appalachian Basin


Research by the Kentucky, Ohio, and West Virginia Geological Surveys has refined the stratigraphic framework of a Cambrian extensional basin underlying the Appalachian Basin. This graben, called the Rome Trough, is filled with up to 9,000 ft of pre-Knox Group sedimentary rocks. Well log analysis and sample descriptions allowed correlation of the Cambrian Conasauga Group north from outcrops along the Eastern Tennessee Overthrust, across parts of eastern Kentucky, and into the Rome Trough. Regional distribution of these formations and the underlying Rome Formation is controlled by extensional faults that were active during and after Conasauga deposition.

To identify the source of hydrocarbons produced from various Cambrian completions in eastern Kentucky and southern West Virginia, numerous Cambrian shale samples were analyzed from across the Rome Trough. Total organic carbon content of these shales was less than 1 percent for all samples, exception for a core of Rogersville Shale from the Exxon No. 1 Smith well in Wayne County, W.Va. TOC for the Rogersville Shale in this core ranges from 1.2 to 4.4 percent, with Tmax values of 460 to 469oC. Six additional Rock-Eval analyses from the Smith core confirmed the original data, with TOC of 1.2 to 4.75 percent, and Tmax of 446 to 460oC. Low hydrogen indices and Tmax data indicate a thermal maturity in the wet gas-condensate window. The Rogersville Shale is a dark gray fissile shale, interbedded with thin laminated and bioturbated siltstone. Hydrocarbon extracts from the No. 1 Smith core are geochemically very similar to produced condensate from Elliott and Boyd County, Ky., and suggest the Rogersville was the source of gas and condensate in the Homer Field.

Challenges in developing a Rogersville Shale play include interpreting structure and stratigraphy in the deeper fault-segmented parts of the Rome Trough and predicting the distribution of organic-rich intervals. The Rogersville Shale ranges in thickness from under 200 to around 1,200 ft, and in depth from approximately 5,500 to 18,000 ft below surface. Interest in the unconventional resource potential of the Rogersville is increasing; eight deep tests have been permitted in the last 18 months.