Date of Graduation
Eberly College of Arts and Sciences
Geology and Geography
The mechanical stratigraphy of the Upper Ordovician Utica Shale is characterized by studying outcrops and core located in Montgomery County, eastern New York State. Previous studies of the Utica Shale in New York State have focused on characterizing fracture orientations, distinguishing fracture generations, and establishing a relationship between fracture density and proximity to faults, but fractures in outcrops of the Utica Shale have not been studied in the context of mechanical stratigraphy. The composition, sedimentary texture, strength, and thickness of individual beds within the Flat Creek Shale and Dolgeville Formation are studied to better understand the nature of fracture propagation in thinly-bedded mudrocks. The Flat Creek Shale and Dolgeville Formation are fine-grained clastic rocks containing varying amounts of detrital carbonate grains. There are also multiple bentonite layers within both members. A fracture bedding termination analysis is conducted at three outcrops of the Flat Creek Shale to identify mechanical interfaces in the vertical section. A Schmidt Hammer is used to measure rock strengths approximately every .2 vertical meters, and samples are collected throughout the section to be analyzed with XRD. Utica Core 74 NY-05 is described in terms of bedding thicknesses, lithofacies, and sedimentary texture. Three thin sections are analyzed with multiple petrographic microscopes to identify common textures and mechanical flaws associated with individual lithofacies. The combination of the fracture bedding termination analysis, rock strength measurement, core description, petrographic investigation, and XRD analysis assist with characterizing the mechanical behavior of these rocks. The fracture bedding termination analysis indicates that bentonites are responsible for approximately 51% of identifiable fracture terminations in the Flat Creek Shale; therefore bentonites act as mechanical barriers to fracture propagation. The bentonites exhibit significantly lower present day rock strength values and are primarily composed of clay minerals. While the remaining 49% of vein-filled fracture terminations occur in shale layers, there are few shale mechanical interfaces identified. The observation that bentonite horizons form significant mechanical barriers to fracture propagation has important implications for modeling subsurface fracture networks, because bentonites are widespread in basins, and are easily distinguished on gamma ray logs.
Brockman, John, "Mechanical Stratigraphy of the Utica Shale, Eastern New York State" (2014). Graduate Theses, Dissertations, and Problem Reports. 5260.