ICDP Scientific Drilling Workshop:
Deep Geothermal Test Borehole, Cornell Campus: 8-10 January, 2020
A 3-day scientific borehole planning workshop sponsored by the International Continental Scientific Drilling Program (ICDP) convened on the Cornell campus in Ithaca, New York State, 8-10 January 2020. The workshop brought together scientists and engineers – students, early career, and senior – who have technical interest in the underlying mechanical response of heterogeneous, low porosity rocks to stress perturbations caused by fluid injection or by natural phenomena, and/or an interest in the materials in the crust of eastern North America.
Participants brought expertise spanning the fields of rock mechanics, hydrogeology, seismology, borehole engineering, geothermal energy engineering, and regional geology of northeastern North America. Participants come from several European countries, Japan, China, many parts of the United States, and several disciplines at Cornell University.
Setting and motivation
Cornell University is advancing a plan to drill a test geothermal borehole to 2.5 – 5 km depth, traversing 3 km of lower Paleozoic sedimentary rock and 1 to 2 km of mid- to high-grade Grenville metamorphic basement, at temperatures expected to be less than 120°C. The university seeks to extract geothermal energy for “direct use” to heat campus buildings, thereby to replace fossil fuels. A pilot borehole should be planned to test reservoir conditions and to minimize risks, both of which require an understanding of the mechanical conditions of the solid rocks and fluids. The rock mechanics problem at the core of Cornell’s aspiration not only has numerous societal implications through energy technologies, but also is fundamental to natural earth deformation. This “borehole of opportunity” will be suitably located for examination of the variability in mechanical response of heterogeneous, low porosity rocks to stress perturbations caused by fluid circulation, to enable investigation at the spatial scale of the natural variability of lithology, fabric, and inherited fractures.
This ICDP workshop contributed greatly to developing a borehole science plan
The Workshop was dedicated to developing a set of borehole experiments and tests that extends beyond the minimum needs of a Cornell site assessment, to be the basis for improving and testing general models of subsurface mechanical regimes. The suite of experiments discussed and outlined in a preliminary fashion would:
1). Improve understanding of fracture-dominated fluid flow and the thermo-poroelastic response within rocks at depths greater than 2 km, of varying bulk properties and varying categories of fractures.
2). Document the mechanical state and poroelastic properties of variable lithologic categories of mid- to high-grade metamorphic rock and low porosity sedimentary rock under the conditions of pressure manipulation needed to produce geothermal heat
3). Better understand the properties and conditions that influence technical uncertainties associated with intentionally circulating fluids through fractured basement rocks
Formal scientific reports on the conference discussions and recommendations are being drafted. A proposal to the Department of Energy for the basic drilling and most central experiments has been submitted. If successful, additional proposals for refined experiments also need to be developed and submitted to suitable agencies and organizations.
Teresa Jordan, Regional geology and sedimentary basins; Cornell University, USA
Patrick Fulton, Thermal and hydraulic geophysics; Cornell University, USA
Jefferson Tester, Geothermal systems engineer; Cornell University, USA
Ernst Huenges, geothermal energy and geophysics; GFZ German Research Centre for Geosciences, Germany
David Bruhn, Geothermal engineering and rock mechanics; Technical University Delft, Netherlands/GFZ, Germany
Hiroshi Asanuma, Geothermal engineering; National Institute of Advanced Industrial Sciences and Technology, Japan