Geothermal energy is a clean, renewable source of energy found in Earth’s subsurface. There is inherent financial risk in the exploration and production of geothermal energy, primarily due to the high cost of drilling and the uncertainty in reservoir flow properties. Repurposing existing data from the petroleum industry has the potential to reduce uncertainty in geothermal exploration, and may lead to the identification of suitable geothermal prospects in Earth’s widespread sedimentary basins. The Appalachian Basin of the eastern United States provides an opportunity for investigating the potential for low-temperature geothermal energy production, via the reanalysis of existing petroleum reservoir data. A probabilistic analysis of over 1,000 petroleum reservoirs concludes that most hydrocarbon reservoirs in the Appalachian Basin are not suitable for geothermal applications. Furthermore, a validation of these results using natural gas production data concludes that the traditional Productivity Index is not a suitable model for fractured or vuggy lithologies. However, one of the most promising plays in the region is the Trenton-Black River hydrothermal dolomite reservoirs in the Southern Tier of New York. Extensive analysis of existing datasets from a key reservoir in the play—Quackenbush Hill—reveals a highly fractured, heterogeneous, vuggy reservoir with temperatures ~90°C, high horizontal permeability, negligible vertical permeability, and opportunities for stimulation. Assuming these reservoir features are similar for the remainder of T-BR reservoirs, this play has great promise for a petroleum-to-geothermal transition. Finally, a petrographic analysis of matrix and cements from a T-BR structural outcrop analog is conducted to determine the outcrop’s diagenetic similarity to the subsurface reservoirs. The analysis suggests that the outcrop is a diagenetic analog to the subsurface reservoirs, allowing for an application of fracture knowledge from the surface outcrop to the sub-surface T-BR reservoirs. A fracture analysis of that same outcrop provides a better understanding of the fracture spacing in the subsurface, which informs a conceptual model of potential fluid flow in the T-BR reservoirs for future research to more accurately model and predict the flow of geothermal fluids through the T-BR reservoirs.