| Title | Preliminary Hydrogeologic Characterization of the Cornell University Borehole Observatory (CUBO), Ithaca NY |
|---|---|
| Authors | Roberto D. CLAIRMONT, Patrick M. FULTON, Teresa E. JORDAN |
| Year | 2023 |
| Conference | Stanford Geothermal Workshop |
| Keywords | hydraulic diffusivity, permeability, model, pressure diffusion, Cornell University, deep direct-use, dual-packer, hydrogeologic air-lift test, reservoir. |
| Abstract | The Cornell University Borehole Observatory is a 9790 ft deep well drilled into Pre-Cambrian basement for the purpose of identifying the feasibility of deep direct-use district heating (DDU) of the Cornell Campus via a DDU geothermal system. This follows Cornell’s objective to obtain a carbon neutral campus by the year 2035. To incorporate such a system, target reservoir formations at depth should provide adequate temperature and fracture permeability for injection and production at a flow rate that will maintain a suitable lifetime of the reservoir. One of the primary objectives is to understand the hydrological properties of target formations. Here we present data and initial findings obtained from several tests that provide insights into the subsurface hydrogeologic characteristics. Following completion of drilling in mid-August 2022, several days of logging and testing were conducted within the open section of the borehole (7656 - 9790 ft). Acoustic and resistivity image logs from borehole imaging (BHI) indicate the presence of fractures, identifying regions of interest where sufficient fracture permeability may exist. Near the end of operations, production and injection tests were conducted in the full borehole. First an airlift test was conducted that progressively lowered the borehole water level to ~4000’ below ground surface. Based on observations of water level and P-T logs run during and after the test, the borehole did not appear to produce significant flow. Reinjection of the displaced water and pressurization with mudpumps up to 1400 psig, also did not appear to drive considerable flow into the formation. These data suggest the formations spanning the Ordovician-Pre-Cambrian strata are relatively low permeability. However, there are indications of localized fracture permeability and connectivity based on correlative signatures from several other logs and tests. For instance, online gas analysis by mass spectrometer during drilling reveals numerous intervals with inflows of inorganic gases, particularly Hydrogen and Helium. The depth interval with the highest fluxes corresponds with fracture networks identified within dolomitized sandstone units within the Galway Formation between depths 8670 – 8710 ft depth. Dual packer experiments, primarily used for minifrac tests and stress analysis targeted fractures identified at 8685 and 8695 ft and show evidence of fracture permeability – at least when borehole fluid pressures are relatively high. Analyzing the diffusion of pressure during these experiments provides constraints on hydraulic diffusivity within one of the target intervals under investigation for potential development as an EGS reservoir. |