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Geologic Variability Within the Marcellus Shale and its Relationship With Natural Fractures


Within the Appalachian Basin, the Marcellus Shale is being exploited as a natural gas resource. Primary sedimentary characteristics of the rock, inclusive of mineralogy, organic matter abundance, and fabric play key roles in determining the manner in which fractures propagate through the rock, whereas trace element content may impact produced water chemistry. Uncertainty exists regarding the degree of spatial variability of these primary features at both local and regional scales. Using outcrop and laboratory analysis, this study attempts to spatially characterize heterogeneity within the Union Springs Formation. Expanding upon the framework provided by Karaca (2012)* for the fine-scale characterization of the Union Springs, this study provides detailed descriptions of three full Union Springs columns exposed in quarries and 105 associated samples. The data capture rock properties and document their variability at distances ranging between 160 m and 39,000 m distance from the reference column. Packages of rock possessing properties suggestive of specific depositional environments are organized into microfacies, based upon characteristics such as organic carbon abundance, trace element abundance, and mineralogical distribution. Quarry and core data also describe existing fracture planes (orientation, aperture, mineral fill, spacing, length) within the rock. These fracture data will be used to document and correlate changes or trends of fracturing to the microfacies identified within the rock. In addition to the previously-defined microfacies, additional microfacies are emerging at the most distant column location. Fracture characteristics are expected to vary across microfacies boundaries within each column, as mechanical properties differ between microfacies. *Karaca, C. 2012, Characterization of the Union Springs Formation, Finger Lakes Region, NY: an integrated high resolution facies, geochemical and sequence stratigraphical approach (MS thesis): Cornell University, 92 p.