47th Annual AAPG-SPE Eastern Section Joint Meeting

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Methods to Assess Thermal Maturity of the Utica / Point Pleasant Play in the Appalachian Basin


Thermal Maturity has been a key component of the Utica play since its inception. The initial focus was determining the oil, condensate, wet gas, and dry gas boundaries in Eastern Ohio and Western Pennsylvania. While that aspect of the play is now well delineated, there is still work to do determining the effective extent of the dry gas play as it extends into Central and Northeastern Pennsylvania. Vitrinite Reflectance (VRo %) measurements are the gold standard for assessing maturity in coals and source rocks. The Utica and Point Pleasant are Upper Ordovician in age, so unfortunately there is no vitrinite to measure. Conodont Alteration Index (CAI) maps introduced by Harris and others (1978) and updated by Repetski (2008) have helped in determining the overall maturity patterns in the Appalachian Basin. However, the author believes the CAI is an unreliable metric to accurately define the boundary between the dry gas and over mature parts of the play. Using logs, cuttings, and core samples collected throughout our 100+ year history in the Appalachian Basin, Seneca has undertaken a number of studies to further our knowledge of the extents of the deep, dry gas Utica play. These efforts include looking at bitumen and graptolite reflectance, resistivity logs, and Raman Spectroscopy, in addition to integrating shallower datasets from Devonian source rocks and Pennsylvanian coals. This presentation will detail the advantages, as well as issues, encountered with each of these methods.