An introduction to the EGS Collab project

The development of Enhanced Geothermal Systems (EGS) requires an ability to accurately predict the flow rates and temperatures of the production wells. While simple in concept, EGS is complicated by the heterogeneity and complexity of fracture pathways that can lead to channeling, short-circuiting, and premature thermal breakthrough. The EGS Collab project will establish a suite of intermediate-scale (~10-20 m) field test beds coupled with stimulation and interwell flow tests that will provide a basis to better understand the fracture geometries and processes that control heat transfer between rock and stimulated fractures. As such, the EGS Collab experiments will provide a relatively inexpensive means of testing tools and concepts that could later be employed under geothermal reservoir conditions at FORGE. Our tests will be well-controlled, in situ experiments focused on rock fracture behavior and permeability enhancement. Pre- and post-test modeling of each test will allow for model prediction and validation. Comprehensive instrumentation will be used to collect high-quality and highresolution geophysical and other fracture characterization and fluid flow data, and these data will be analyzed and compared with models and field observations to further elucidate the basic relationships between stress, induced seismicity, and permeability enhancement. To the maximum extent achievable, we will observe and quantify other key governing parameters that impact permeability, and attempt to understand how these parameters might change throughout the development and operation of an EGS project with the goal of enabling commercial viability of EGS. Evaluation of site criteria led the team to choose the Sanford Underground Research Facility (SURF) in South Dakota as the EGS Collab project experimental site. Our team is well underway with designing the first field experiment planned for this project, which is supported by the US Department of Energy’s Geothermal Technologies Office.