The EGS Collab Project – Stimulations at Two Depths

Abstract

The EGS Collab project, supported by the US Department of Energy, is performing intensively monitored rock stimulation and flow tests at the 10-m scale in an underground research laboratory to address challenges in implementing enhanced geothermal systems (EGS). Data and observations from the field tests are compared to simulations to understand processes and build confidence in numerical modeling of the processes. Experiment 1 examined hydraulic fracturing in a well-characterized fractured phyllite 1.5 km deep at the Sanford Underground Research Facility (SURF). Testbed characterization included fracture mapping, borehole acoustic and optical televiewers, full waveform sonic, conductivity, resistivity, temperature, campaign p- and s-wave investigations and electrical resistance tomography. Borehole geophysical techniques including passive seismic, continuous active source seismic monitoring, electrical resistance tomography, fiber-based distributed strain, distributed temperature, and distributed acoustic monitoring, were used to carefully monitor stimulation events and flow tests. More than a dozen stimulations and nearly one year of flow tests were performed. Quality data and detailed observations were collected and analyzed during stimulation and water flow tests, and these data are available. We achieved adaptive control of the tests using real-time monitoring and rapid dissemination of data and near-real-time simulation. Experiment 2 examines the potential for hydraulic shearing in amphibolite 1.25 km deep at SURF. The testbed consists of nine subhorizontal boreholes, four of which surround the testbed with grouted-in ERT, seismic sensors, CASSM and distributed fiber sensors. The test wells include a “five-spot” set with an injection well and four production/monitoring wells. Like Experiment 1, the testbed was characterized geophysically and hydrologically, and three stimulations have been performed using new tools.