THE POWER OF COLLABORATION – TEAM SCIENCE TO ADDRESS KEY QUESTIONS FOR ENHANCED GEOTHERMAL SYSTEMS: THE EGS COLLAB PROJECT

The 2019 U.S. Department of Energy's Geovision study highlighted the vast potential of enhanced geothermal systems (EGS) as a clean and sustainable energy source, as hot rocks are present at depth over much of the United States. However, key challenges remain to be addressed to permit large scale deployment of EGS, including improving understanding of the stimulation of crystalline rock to create appropriate flow pathways to facilitate heat exchange and the ability to effectively simulate both the stimulation and the flow and transport processes in the resulting fracture network. The EGS Collab project team consists of scientists and engineers from ten national laboratories, eight universities, and several private companies, and is using the Sanford Underground Research Facility (SURF), the former Homestake gold mine, in Lead, SD, to conduct a suite of experiments in intermediate-scale (~10 - 20 m) field test beds to investigate fracture stimulation and flow between wells in crystalline rock. The test beds consist of arrays of well characterized boreholes (for injection, production, and monitoring) at depths within SURF (1.25-1.5 km) that provide realistic stress conditions. The monitoring boreholes are densely instrumented to constrain the stimulation and flow experiments, which are focused on characterizing and understanding the interactions between rock fracture behavior, seismicity, and permeability enhancement. Coupled process simulations are developed for these field tests to compare experimental observations to model predictions and allow for validation. The team recently completed a suite of experiments in a test bed on the 4850 level (~1.5 km depth) that involved the creation of hydraulic fractures. Long term flow tests examined the interaction of these fractures with natural fractures to create dynamic flow pathways between the injection and production boreholes, which serve to facilitate heat exchange between the rock mass and the circulating water. The team is developing a new test bed on the 4100 level (~1.25 km depth) that will focus on shear stimulation of favorably oriented fractures. The success of the research conducted to date is based upon the collaborative efforts of the team and the integration of many experimental components into a series of conceptual and coupled process models.