DETERMINING THE FACTORS THAT CONTROL NATURAL FRACTURE CHARACTERISTICS IN THE APPALACHIAN PLATEAU

Natural fractures play a critical role in a number of socially relevant and geologically significant problems. Importantly, the flow of geologic fluids (e.g. groundwater, hydrocarbons) through rock is controlled by the properties of the rock matrix and the properties of any deformation features. For example, natural fractures can affect the direction that groundwater flows and impact the migration of contaminants in the subsurface. Natural fractures are also important for hydrocarbon production, and an understanding of these features can be critical for safe and efficient production of oil and gas. However, there is currently no reliable way to accurately predict the location or characteristics of natural fractures in the subsurface.

This study analyzed natural fractures in drill core, outcrop, and geophysical logs taken from sites in the Northern Appalachian Plateau (Pennsylvania and New York) in order to produce a regional characterization of natural fractures at various depths and in multiple lithologies. We examined the effects of modern day depth, rock type, and tectonic history on the development of the fracture network in the Northern Appalachian Plateau and were able to characterize families of fractures that can serve as a guide for future research. The fracture network present within these rocks is the result of both Alleghenian Tectonics and the post-Alleghenian tectonic history of the region (including the modern day stress field). Fracture characteristics can also be used to associate families of fractures with large scale tectonics. Additionally, some groups of fractures can be more commonly found in specific lithologies and at certain depths. Regardless of the age of a rock, the rocks in the shallow part of the subsurface (0-100m) are more likely to contain fractures that are oriented parallel to the modern day stress field, while fractures deep within the earth (300-2000m) reflect Alleghenian shortening. By expanding on these results with future research, it may be possible to improve our abilities to predict fracture characteristics prior to drilling.