Thermal maturity of northern Appalachian Basin Devonian shales: Insights from sterane and terpane biomarkers

► Northern Appalachian Basin Devonian shales are an important source rock. ► Vitrinite reflectance underestimates thermal maturity in early mature Devonian shale. ► Misidentification of solid bitumen as vitrinite may be a significant problem. ► Biomarker ratios suggest most samples are mature with r...

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Bibliographic Details
Published in:Fuel (Guildford) 2013-04, Vol.106, p.455-462
Main Authors: Hackley, Paul C., Ryder, Robert T., Trippi, Michael H., Alimi, Hossein
Format: Article
Language:English
Subjects:
Applied sciences
Basins
Biomarkers
Coal
Devonian shale
Energy
Energy. Thermal use of fuels
Exact sciences and technology
Fuels
Gas chromatography–mass spectrometry
Geochemistry
Kerogen
Reflectance
Reflectivity
Rock
Shale
Thermal maturity
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Summary:► Northern Appalachian Basin Devonian shales are an important source rock. ► Vitrinite reflectance underestimates thermal maturity in early mature Devonian shale. ► Misidentification of solid bitumen as vitrinite may be a significant problem. ► Biomarker ratios suggest most samples are mature with respect to hydrocarbon generation. To better estimate thermal maturity of Devonian shales in the northern Appalachian Basin, eleven samples of Marcellus and Huron Shale were characterized via multiple analytical techniques. Vitrinite reflectance, Rock–Eval pyrolysis, gas chromatography (GC) of whole rock extracts, and GC–mass spectrometry (GCMS) of extract saturate fractions were evaluated on three transects that lie across previously documented regional thermal maturity isolines. Results from vitrinite reflectance suggest that most samples are immature with respect to hydrocarbon generation. However, bulk geochemical data and sterane and terpane biomarker ratios from GCMS suggest that almost all samples are in the oil window. This observation is consistent with the presence of thermogenic gas in the study area and higher vitrinite reflectance values recorded from overlying Pennsylvanian coals. These results suggest that vitrinite reflectance is a poor predictor of thermal maturity in early mature areas of Devonian shale, perhaps because reported measurements often include determinations of solid bitumen reflectance. Vitrinite reflectance interpretations in areas of early mature Devonian shale should be supplanted by evaluation of thermal maturity information from biomarker ratios and bulk geochemical data.
ISSN:0016-2361
1873-7153
DOI:10.1016/j.fuel.2012.12.032