| Title | The EGS Collab – Initial Results from Experiment 2: Shear Stimulation at 1.25 Km Depth |
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| Authors | Tim KNEAFSEY, Doug BLANKENSHIP, Pat DOBSON, Joseph P. MORRIS, Mark WHITE, Pengcheng FU, Jeff BURGHARDT, Bill ROGGENTHEN, Paul C. SCHWERING, EGS Collab Team |
| Year | 2022 |
| Conference | Stanford Geothermal Workshop |
| Keywords | Stimulation, crystalline rock, field test, simulation, flow test, geophysics |
| Abstract | The EGS Collab project is performing intensively monitored rock stimulation and flow tests at the 10-m scale in an underground research laboratory to inform challenges in implementing enhanced geothermal systems (EGS). This project, supported by the US Department of Energy, is gathering data and observations from the field tests and comparing to understand processes and to build confidence in numerical modeling of the processes. The now-completed Experiment 1 examined hydraulic fracturing in an underground test bed at the Sanford Underground Research Facility (SURF) in Lead, South Dakota, at a depth of approximately 1.5 km. We installed geophysical monitoring instrumentation in six of eight sub-horizontal boreholes in a well-characterized phyllite with many sensor types to allow careful monitoring of stimulation events and flow tests. The other two boreholes were also instrumented to perform and carefully measure water injection and production. We performed more than a dozen stimulations and nearly one year of flow tests in the testbed and collected and analyzed detailed observations and numerous data sets of processes occurring during stimulation and dynamic flow tests. Data from these tests are generally openly available. Ambient temperature and chilled water flow tests were performed with many tracer tests to examine system behavior. We achieved adaptive control of the tests using close monitoring of rapidly disseminated data and near-real-time simulation. Numerical simulation was used to answer key experimental design questions, to forecast fracture propagation trajectories and extents, and to analyze and evaluate results. Many simulations were performed in near-real-time in conjunction with the field experiments, with more detailed simulations performed on a longer timeframe. Experiment 2 is designed to examine hydraulic shearing in a new test bed at SURF at a depth of about 1.25 km in amphibolite under a different set of stress and fracture conditions than Experiment 1. A testbed is nearly complete consisting of 9 boreholes, in addition to two earlier-drilled characterization boreholes. Of the 9 boreholes, one is used for injection, four contain grouted instrumentation, and the remaining four are adaptively used for production and monitoring. The testbed construction optimized encounters with approximately five fracture set orientations. The testbed geology, hydrology, and geomechanical conditions are described, in addition to a descrption of the monitoring system, stimulation and flow system, and planned stimulations. |