COMPARING THE SPATIAL DISTRIBUTION AND CHARACTERISTICS OF FRACTURES IN OUTCROP AND CORE IN THE APPALACHIAN BASIN

There is significant interest in studying fractures within sedimentary basins, as these features impact subsurface fluid flow and cross-formational fluid migration. While progress has been made in understanding fractures found in outcrop, it is difficult to determine if outcrop serves as a reliable tool for subsurface fracture analysis. As a result, there is great uncertainty concerning the spatial distribution of fractures in the subsurface. Resolving these uncertainties will improve our ability to predict fracture characteristics and accurately model subsurface fluid flow. This study examines how fractures vary with depth in the Appalachian basin, whether fracture characteristics and lithology are related in sedimentary rocks, and whether topography impacts fracturing.

Eight drill cores and multiple outcrops are examined from across the Appalachian Plateau in Pennsylvania and New York, United States. The age of these rocks ranges from Pennsylvanian to Late Devonian, and the rock examined is primarily limestone, mudstone, coal, and sandstone. Natural and induced fractures are observed in all the cores. In outcrop, the most commonly observed fractures were steeply dipping joints and occasional veins. In core, the dip angle of natural fractures varies greatly, from horizontal to steeply dipping, with horizontal fractures being the most common. Fractures found in core include minor faults, shear fractures, joints, veins, and iron-oxide stained fractures. This study confirms that a correlation between depth and fracture intensity exists within core. Moreover, lithology has a strong impact on fracture characteristics. These results suggest that both past tectonics and modern-day process impact fracturing, and highlight the differences between fractures found at depth, and those found near the surface.