Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Appalachian Basin Database for Devonian Gas Shales
(1) Eastern Energy Resources Science Center, U.S. Geological Survey, Reston, VA.
The U.S. Geological Survey (USGS) in cooperation with the State Geological Surveys of Virginia, West Virginia, Kentucky, Ohio, Pennsylvania, and New York has prepared an organic geochemistry database for the Devonian shales of the Appalachian basin. The database consists of previously published data and new data from samples submitted by the states for analyses. In general, the samples are analyzed for percentage of total organic carbon (TOC), vitrinite reflectance (Ro), and Rock Eval. In addition selected samples were analyzed for visual kerogen and thermal alteration indices (TAI). Conodont color alteration indices (CAI) have been analyzed for some previously published sample sets. The database provides information that will readily assist in the future assessment and development of the hydrocarbon resources of the Appalachian basin. For example, basin modeling data, together with older geochemical data corrected for vitrinite suppression, and new thermal maturation data, suggest that the 0.6 %Ro isoline is farther to the west in Ohio than the 0.6% isoline used to define Assessment Unit boundaries for the USGS 2002 assessment. This places much of the area underlain by Devonian shale in central Ohio within the oil generating window, and our assessment unit boundaries must be adjusted accordingly. In contrast, much of western Pennsylvania and adjacent West Virginia are underlain by shale source rocks that range from about 1 to 3 percent Ro.
Similarly, TOC data show that the Huron Shale of Ohio, West Virginia, and Virginia, and the Ohio Shale of Kentucky are the richest source rocks in the Appalachian basin, where they are in the oil generating window. In comparison, the Marcellus Shale is not quite as rich in organic carbon as the Huron and Ohio Shales, and where it is more deeply buried within the gas-generating window much of its algal organic material has been converted to gas. Similarly, the Rhinestreet Shale of West Virginia, Ohio, and Virginia, and other Devonian shales of Virginia have a significantly lower content of organic carbon than the Marcellus.