| Title | Risk Reduction in Geothermal Deep Direct-Use Development for District Heating: A Cornell University Case Study |
|---|---|
| Authors | J. Olaf GUSTAFSON, Jared D. SMITH, Stephen M. BEYERS, Jood A. AL ASWAD, Teresa E. JORDAN, Jefferson W. TESTER, Tasnuva Ming KHAN |
| Year | 2019 |
| Conference | Stanford Geothermal Workshop |
| Keywords | economic risk, LCOH, district heating, deep direct-use, heat pumps, cascading use, low temperature, geothermal reservoir modeling, surface use modeling, uncertainty analysis, thermal storage |
| Abstract | Cornell University in Ithaca, NY is potentially well-suited for a deep direct-use (DDU) geothermal heating system to serve our campus of ~30,000 people in more than 14 million sq. ft. of buildings. The heating demand for the existing natural-gas-fed district heating system is ~240,000 MWth-hrs/yr; successful integration of DDU at Cornell would serve as a model for similar institutions and communities in cold-climate locations. Our current feasibility study focuses on risk reduction through joint analysis of two key aspects of developing a DDU system: 1) uncertainty quantification for reservoir modeling, and 2) surface-use options. We identify a range of coupled subsurface reservoir and surface-use scenarios for successful DDU implementation based on modeled estimates of heat production from the subsurface reservoir and a menu of flexible surface use options. Quantifying uncertainty and constraining values of geologic properties is a necessary component of reservoir modeling. Lacking direct drilling data for the deep ( more than 1 km) bedrock beneath Ithaca, we rely on petrophysical and stratigraphic analysis of well logs and reported cuttings from drilling performed regionally into the sedimentary basin rocks to estimate potential sedimentary reservoir properties. For potential crystalline basement rock targets (2.8-4.5+ km), which are essentially undrilled in our region, we have undertaken studies of Adirondack surface exposures of crystalline rocks considered to be analogs to the basement rocks beneath Ithaca. Multiple options for the surface-use system to accommodate a range of subsurface temperatures and flow rates have been identified using a custom surface-use model we developed for the Cornell campus. The model is grounded in extensive granular energy use records for campus facilities, and includes options for cascaded thermal loads at a variety of temperatures, thermal storage, and the use of water-source heat pumps to extract additional heat at high COPs as a final cascaded use before reinjection to the reservoir. Our models demonstrate that reasonable adjustments in design and operating conditions of surface systems could create a more than 10-fold improvement in heat output from a modest geothermal resource. While this result varies with each arrangement of subsurface resource and surface use design, our work suggests that determining the break-even point for DDU of low-temperature geothermal resources may rely more on an understanding of how heat can be beneficially used at the surface than on moderate differences in reservoir production. This type of integrated analysis can reduce DDU development risk by identifying positive value scenarios for a range of potential reservoir heat production rates at locations where subsurface data are limited. |