EVALUATING SUBSURFACE FRACTURES IN THE APPALACHIAN BASIN

Geoscientists are unable to accurately predict the location and characteristics of subsurface fractures prior to drilling. This is problematic because fractures can impact subsurface fluid flow. Improving our ability to predict fluid flow is important for the management of natural resources like hydrocarbons and groundwater, and can increase our understanding of contaminant migration. Past research on fractures found at the surface has revealed that some lithologies are more likely to contain fractures. However, this relationship has not been adequately explored in the subsurface, and we know little about how modern-day depth and fracture characteristics relate.

This study examines underground fractures in continuous drill core taken from the surface through over 300m in depth. The goal of this research is to explore correlations between fracture characteristics and modern-day depth, lithology, and rock properties in the Appalachian Basin. The core used for this project was drilled from the Appalachian Basin in Norwich, Pennsylvania, United States and is composed of rocks from the Pottsville Formation through the Lock Haven Formation, placing its age between Late Devonian and Pennsylvanian. The primary lithology of the core consists of sandstone, shale, and mudstone. Both natural and drilling-induced fractures have been observed, with the natural fractures being composed primarily of minor faults, veins, and iron-oxide stained fractures. In general, the density of fractures decreases with depth. Fractures exhibit some correlation with lithology, and veins are more common in limestones. The dip angle of the natural fractures varies from horizontal to steep. The data suggests that there is a relationship between present-day depth and fracturing, with rock properties also playing a critical role.