PNNL

Abstract

Development of Enhanced Geothermal Systems (EGS) requires accurate predictions of flow rates and temperatures at production wells over time. The concept of EGS is simple; however, complications from heterogeneity and complexity of fracture pathways may lead to channeling, short-circuiting, and premature thermal breakthrough. In the EGS Collab project, we are establishing a suite of highly monitored and well characterized intermediate-scale (~10-20 m) field test beds along with fracture stimulation and interwell flow tests to better understand processes that control formation of effective subsurface heat exchangers. EGS Collab experiments will provide a means of testing tools and concepts that could later be employed under geothermal reservoir conditions at FORGE or elsewhere. Key to the project is using numerical simulations in the experiment design and interpretation of results. Our tests will be well-controlled, in situ experiments focused on rock fracture behavior and permeability enhancement. Our pre- and post-test modeling results of each field experiment compared with detailed measurements will allow for improved model prediction and validation. We will use comprehensive instrumentation to collect high-quality and high-resolution geophysical and other fracture characterization and fluid flow data. We will analyze these data and compare them with models and field observations to further elucidate the basic relationships between stress, induced seismicity, and permeability enhancement. We will also observe and quantify other key governing parameters that impact permeability, and will attempt to understand how these parameters might change throughout the development and operation of an EGS project with the ultimate goal of enabling commercial viability of EGS. Our first set of experiments will be performed at the Sanford Underground Research Facility (SURF) in South Dakota. Our team is well underway with building the first field experiment test bed planned for this project, which is supported by the US Department of Energy’s Geothermal Technologies Office.