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Deformation Within the Utica/Pt Pleasant Reservoir, Northern Pennsylvania and Southern New York: A Case for Seismogenic Origin


The Upper Ordovician Utica/Pt Pleasant interval in north-central Pennsylvania has seen significant hydrocarbon exploration and development since 2012. Ongoing activity has provided an inventory of penetrations through an interval previously represented by only a handful of data points. These new data provide detailed information at depth across a large gap in the historical subsurface dataset. Core from Seneca Resources’ DCNR 007 94H revealed an interval of severely deformed bedding approximately 25 feet (8 meters) thick within the gross reservoir interval of the Utica/Pt Pleasant. This zone is characterized by soft sediment deformation (load structures, possible flame structures), fracturing and brecciation of carbonate-rich zones, significant swings in dip. Bed boundaries immediate above and below this zone return to abruptly to flat bedding. This zone of deformation has been found in other wells throughout north-central Pennsylvania. This paper characterizes the deformed zone in Seneca Resources’ wells using a deformation rating scheme. We also trace the aerial extent of the deformation zone over a multi-county area using data from whole core, wellbore image logs, and - with somewhat less confidence - triple combo well logs. The result is an isopachous map that ranges in thickness from over 30 feet to null across several counties in Pennsylvania and New York. Lastly, we seek to constrain the timing of the deformation interval usinga vertical profile of dC13 measurements from inorganic carbon. Given the nature of deformation observed in well data (core and image logs) and the spatial distribution and thickness of the interval of interest, a seismogenic origin is the leading contender for this zone within an active hydrocarbon play.