EGS COLLAB PROJECT: STIMULATION AND SIMULATION OF CRYSTALLINE ROCK (Invited Presentation)

To implement enhanced geothermal energy recovery, a better understanding of stimulation and inter-well fracture flow in crystalline rock is needed. The EGS (Enhanced Geothermal Systems) Collab project is performing stimulation and flow tests in highly monitored, well-characterized intermediate scale (~10-20 m) field test beds at a depth of nearly 1.5 km. These tests provide the ability to evaluate concepts, and data to test and validate models to be used for EGS development and at DOE’s Frontier Observatory for Research in Geothermal Energy (FORGE) project. Improving numerical simulators is key to the project, and simulations are used in experiment design and interpretation of results. In Experiment 1, an injection, production, and six monitoring boreholes were first characterized with optical and acoustic televiewers, full waveform seismic, electrical resistivity, natural gamma, and temperature. The test block was further characterized using seismic tomography (compressional- and shear-), electrical resistance tomography (ERT - baseline and flow), and hydrologic characterization including tracer tests. Installed flow and stimulation monitoring systems include: 1) passive seismic monitoring/acoustic emissions; 2) continuous active source seismic monitoring; 3) ERT in conjunction with dynamic electrical imaging using high contrast fluids; and 4) distributed acoustic (DAS), temperature (DTS), and strain (DSS) fiber optic sensors. Fracture aperture strain monitoring is performed using the Step-rate Injection Method for Fracture In-situ Properties (SIMFIP) tool. The detailed site characterization data, together with the array of installed monitoring systems and inversion methods, help constrain the coupled process models. A selection of results from numerical simulations and experiments performed at the Sanford Underground Research Facility (SURF) in South Dakota will be presented. To date, stimulations have been performed at several locations, connecting our injection and production wells and flow tests and thermal tests have been performed. Numerous data sets have been collected and analyzed.