STRESS STATE ANALYSIS AT CORNELL UNIVERSITY BOREHOLE OBSERVATORY (CUBO)
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Cornell University aims to employ geothermal energy as a heat source for its campus. To enable informed decision-making regarding the feasibility of implementing a geothermal system, an exploration well, Cornell University Borehole Observatory (CUBO), was drilled in 2022. CUBO's goal is to characterize the subsurface in order to guide the potential design and development of subsequent wells that could operate as a geothermal doublet within an Enhanced Geothermal System for deep direct use of heat energy. The CUBO well was constructed in five segments and reached a depth of three km (T.D. = 9790.5 ft). In order to optimize the potential of a geothermal reservoir, a precise analysis of in-situ stress is essential. Initial investigations reveal low natural permeability, necessitating a stimulation plan to increase permeability for future stages. This thesis presents a characterization of subsurface stress conditions based on observations and testing within CUBO, as well as a re-analysis of historical stress data from the upstate NY region, specifically the Auburn geothermal well. Stress state analysis is conducted based on borehole logs, dual-packer mini-frac tests, and a comparison of results with offset wells. This work provides an analysis and interpretation of stress orientation and magnitude in CUBO, along with the associated uncertainties. The following key findings highlight the results of this study: 1) In the target zone studied at depths exceeding 7800 ft, it is determined that the maximum horizontal stress direction varies little with depth. Orientations between N 38°E to N 50°E occur in both sedimentary formations and the crystalline basement. 2) The principal stress magnitudes in this interval suggest a strike-slip regime, consistent with stress field indicators elsewhere within the Appalachian Basin of the northeast region of the USA. These results provide valuable insights for the design and stimulation of future wells.
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Olson Hoal, Karin