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Sedimentary basins are attractive for geothermal development due to their ubiquitous presence, high perme ability, and extensive lateral extent. Geothermal energy from sedimentary basins has mostly been used for direct heating purposes due to their relatively low temperatures, compared to conventional hydrothermal systems. However, there is an increasing interest in using sedimentary geothermal energy for electric power generation due to the advances in conversion technologies using binary cycles that allow electricity generation from reservoir temperatures as low as 80 ◦C. This work develops and implements analytical solutions for calculating reservoir impedance, reservoir heat depletion, and wellbore heat loss in sedimentary reservoirs that are laterally extensive, homogeneous, horizontally isotropic and have uniform thickness. Reservoir impedance and wellbore heat loss solutions are combined with a power cycle model to estimate the electricity generation potential. Results from the analytical solutions are in good agreement with numerically computed reservoir models. Our results suggest that wellbore heat loss can be neglected in many cases of electricity generation calculations, depending on the reservoir transmissivity. The reservoir heat depletion solution shows how reservoir tempera ture and useful lifetime behave as a function of flow rate, initial heat within the reservoir, and heat conduction from the surroundings to the reservoir. Overall, our results suggest that in an exploratory sedimentary geothermal field, these analytical solutions can provide reliable first order estimations without incurring intensive computational costs.
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Subsurface Insights from the Cornell University Borehole Observatory (CUBO): A 3km Deep Exploratory Well for Advancing Earth Source Heat Deep Direct-Use Geothermal for District Heating
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 °C. 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. Altogether the knowledge from this information guides decisions regarding the design, depth, and orientation of subsequent injection and production wells at Cornell, as well as highlighting University, and highlights particular geologic targets and strategies for developing an effective and efficient enhanced geothermal reservoir. These comprehensive results, as well as lessons learned regarding the overall approach, can help de-risk decisions regarding the development of deep geothermal energy systems both at Cornell University and elsewhere.
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- Award ID(s):
- 2231125
- PAR ID:
- 10567474
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- https://pangea.stanford.edu/ERE/
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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