Open-File Report 2012–1194
Detailed and reconnaissance field mapping and the results of geochemical and mineralogical analyses of outcrop samples indicate that the Devonian shales of the Broadtop Synclinorium from central Virginia to southern Pennsylvania have an organic content sufficiently high and a thermal maturity sufficiently moderate to be considered for a shale gas play. The organically rich Middle Devonian Marcellus Shale is present throughout most of the synclinorium, being absent only where it has been eroded from the crests of anticlines. Geochemical analyses of outcrop and well samples indicate that hydrocarbons have been generated and expelled from the kerogen originally in place in the shale. The mineralogical characteristics of the Marcellus Shale samples from the Broadtop Synclinorium are slightly different from the averages of samples from New York, Pennsylvania, northeast Ohio, and northern West Virginia. The Middle Devonian shale interval is moderately to heavily fractured in all areas, but in some areas substantial fault shearing has removed a regular “cleat” system of fractures.
Conventional anticlinal gas fields in the study area that are productive from the Lower Devonian Oriskany Sandstone suggest that a continuous shale gas system may be in place within the Marcellus Shale interval at least in a portion of the synclinorium. Third-order intraformational deformation is evident within the Marcellus shale exposures. Correlations between outcrops and geophysical logs from exploration wells nearby will be examined by field trip attendees.
First posted October 3, 2012
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Enomoto, C.B., Coleman, J.L., Jr., Haynes, J.T., Whitmeyer, S.J., McDowell, R.R., Lewis, J.E., Spear, T.P., and Swezey, C.S., 2012, Geology of the Devonian Marcellus Shale—Valley and Ridge province, Virginia and West Virginia—A field trip guidebook for the American Association of Petroleum Geologists Eastern Section Meeting, September 28–29, 2011: U.S. Geological Survey Open-File Report 2012–1194, 55 p., available only at http://pubs.usgs.gov/of/2012/1194/.
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