by Hiroshi Asanuma, David F. Bruhn, David F. Bruhn, Ernst Huenges, Teresa Eileen Jordan, Jefferson William Tester

We propose a workshop to outline a science plan for a “hole of opportunity.” Cornell University proposes to drill an exploratory geothermal energy borehole to a depth in the range of 4 - 5 km, which will penetrate nearly 3 km of Paleozoic sedimentary rocks and = 1 km of amphibolite-grade Grenville metamorphic rocks, in central New York state, United States. The proponents of this ICDP workshop proposal envision that this borehole should be a scientific opportunity to gain understanding of how heterogeneous mid- to high-grade metamorphic rocks and low porosity sedimentary rocks respond to pore pressure manipulation. An ICDP Workshop will expand the expertise available to identify the best strategy for obtaining from the borehole the vital samples and measurements required to advance understanding of the mechanical response of heterogeneous, low porosity rocks to stress perturbations. The proposed project has a direct societal value, through the potential to advance use of geothermal energy in broad continental regions, as well as its direct scientific value. The production of small magnitude strain in rock through fluid injection is a practical means for interconnecting porosity to improve fluid flow. However, much attention is currently focused on the growing recognition that fluid injection as part of several types of energy subsurface activity can sometimes trigger earthquakes of sufficient strength to cause damage and public concern. Examples are well known for alternative energy (geothermal), fossil fuel (hydraulic fracturing and wastewater injection), and mitigation technologies (carbon sequestration), yet similar operations operating in many locations have caused no similarly large earthquakes. The conundrum is to predict which intervals of rocks, in which areas, can be stimulated a) successfully, and b) safely. Setting aside energy technologies, the scientific need for improved understanding of mechanical response to pressure perturbations is broader, inclusive of stress perturbations with natural causes. We feel that a Workshop that focuses on designing borehole experiments is essential to provide the basis for improving and validating general models. The proposed Workshop will be convened at Cornell University, preferably in the last quarter of 2019. We will invite an international group of borehole specialists, seismologists, rock mechanics theoreticians and experimentalists, regional geology specialists, and representatives from the drilling industry and geothermal energy industry. The workshop will focus on design of an integrated set of experiments for two days, followed on a third day by preparation of a report, and possibly a proposal, by a sub-group.

• 1).
• To improve understanding of fracture-dominated fluid flow and the thermo-poroelastic response within rocks at 2.5-4.5 km depth of varying bulk properties (variations defined by petrology, layering, metamorphic fabric, and cohesive strength) and varying categories of fractures (variations defined by parameters such as fracture spacing, mineral fills, orientations).
• 2).
• To 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).
• To better understand the properties and conditions that influence technical uncertainties associated with intentionally circulating fluids through fractured basement rocks

Cornell, Geothermal Anomaly, Grenville, New York, North America, U.s.a.

Latitude: 42.44722, Longitude: -76.48306