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Subsurface Stratigraphy and Petrophysical Analysis of the Middle Devonian Interval, Including the Marcellus Shale, of the Central Appalachian Basin; Northwestern Pennsylvania Anne Yanni In the central Appalachian basin, the multiple organic-rich intervals of the Middle Devonian, including the Marcellus Shale, are an emerging large resource play with high economic potential (estimated 1,307 trillion cubic feet of recoverable gas). This resource play was evaluated by examining the patterns of organic-richness, lithology, stratigraphic distribution, and other depositional characteristics. Using logs from wells throughout northwestern Pennsylvania (940 wells) integrated with core data, the subsurface lithostratigraphic boundaries were defined and correlated for the Marcellus and associated units throughout the study area. Past studies of the Middle Devonian interval have not rigorously defined the lithostratigraphic boundaries in the subsurface and instead relied on limited petrophysical criteria (i.e. un-scaled gamma-ray). In this study, the interval was defined in the subsurface by using a multiple well log approach including the following curves: gammaray, bulk density, resistivity, photo electric, and neutron porosity. Using previous studies on organic-rich Marcellus Shale, potential pay intervals were determined and mapped. The high amounts of total organic carbon (TOC) are correlated to more gas-rich intervals and vary significantly, both stratigraphically and spatially. A correlation was observed between uranium content derived from spectral gamma-ray logs and TOC. The relationship among gas content, TOC, and uranium in the Appalachian basin was evaluated using multiple petrophysical analyses techniques. The petrophysical results were used to improve regional and local understanding of the distribution and depositional controls on the Marcellus Shale. Numerous maps and cross sections were constructed to better display local and regional depositional patterns of Middle Devonian units across the central Appalachian basin including the Onondaga Limestone, Marcellus Shale, Mahantango Formation, Tully Limestone, and Genesee Formation. In northwestern Pennsylvania, localized rapid changes in interpreted thick TOC accumulations are tied to local structures. The areas of highest TOC are identified by their relation to the underlying structure at the time of deposition and not by the gross unit thickness of the shale. The accumulation of thick organic-rich Marcellus Shale is interpreted as the interplay of decreased detrital input and increased organic production. These favorable areas appear to be closely related to favorable paleooceanographic conditions such as distance from sediment source and organic production related to paleotopography of the sea floor. These conditions define an exploration fairway through western Pennsylvania in terms of increased gas potential. ACKNOWLEDGEMENTS I would like to thank National Energy Technology Laboratories for funding this research and for providing valuable core data. I would also like to thank Kristin Carter and Jaime Kostelnik from the Pennsylvania Department of Conservation and Natural Resources for their assistance with locating interpreted formation tops and vitrinite reflectance data. I would like to thank my fellow Mountaineers for their constant support and encouragement: Dr. Timothy R. Carr, for accepting me as a student, providing financial assistance, and constantly and consistently guiding me throughout this entire project; Dr. Jaime Toro, for serving as both a professional and personal mentor throughout both my undergraduate and graduate degree programs; Dr. Dengliang Gao, for professional mentoring, supporting this project, and his personal introductions and resulting opportunities with international petroleum companies; and Dr. Matthew L. Boyce, for his constant help with this project and for generously sharing his time, data, skill, and knowledge. I would also like to thank my family for their unconditional love and support, my new husband Rodney for his constant love and kindness, and my Great Uncle William Knight for his interest and encouragement.

Subsurface Stratigraphy and Petrophysical Analysis of the Middle Devonian Interval, Including the Marcellus Shale, of the Central Appalachian Basin; Northwestern Pennsylvania