Motivated by Cornell University's aspiration to use geothermal heat to replace fossil fuels to heat campus buildings, a 3-km deep geothermal exploratory well, the Cornell University Borehole Observatory (CUBO), was drilled on the Ithaca, NY campus in the summer of 2022. CUBO extends through largely low porosity and low permeability Paleozoic sedimentary rocks above low-grade metamorphic basement rocks. In order to assess the potential for and inform the design of an operational deep direct use geothermal system within the US Northeast, the main objective of CUBO is to characterize the subsurface and potential fracture-dominated reservoir targets in both the sedimentary units and basement within a temperature range between 70 – 90+ oC. Here we report results of our analysis which provide insight into the hydrologic, thermal, and mechanical conditions at depth and the associated physical rock fracture properties and characteristics. This integrative work incorporates regional well logs and geologic and geophysical data, as well as the CUBO-specific downhole logging and borehole image data collected during drilling operations, subsequent borehole temperature profiling and fluid sampling, downhole dual-packer mini-frac stress tests, and microstructural and physical property analysis of sidewall cores and cuttings. Together the knowledge from this information guides decisions regarding the design, depth, and orientation of subsequent injection and production wells at Cornell, as well highlights particular geologic targets and strategies for developing an effective and efficient enhanced geothermal reservoir. The overall results as well as the lessons learned and overall approach can help de-risk decisions regarding the development of deep geothermal energy systems both at Cornell and elsewhere.

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