Seismic monitoring of EGS tests at the Coso Geothermal area, California, using accurate MEQ locations and full moment tensors
- Durham Univ. (United Kingdom). Dept. of Earth Sciences
- U.S. Geological Survey, Menlo Park, CA (United States)
- Naval Air Weapons Station, China Lake, CA (United States). Geothermal Program Office
In this study, we studied high-resolution relative locations and full moment tensors of microearthquakes (MEQs) occurring before, during and following Enhanced Geothermal Systems (EGS) experiments in two wells at the Coso geothermal area, California. The objective was to map new fractures, determine the mode and sense of failure, and characterize the stress cycle associated with injection. New software developed for this work combines waveform cross-correlation measurement of arrival times with relative relocation methods, and assesses confidence regions for moment tensors derived using linear-programming methods. For moment tensor determination we also developed a convenient Graphical User Interface (GUI), to streamline the work. We used data from the U.S. Navy’s permanent network of three-component digital borehole seismometers and from 14 portable three-component digital instruments. The latter supplemented the permanent network during injection experiments in well 34A-9 in 2004 and well 34-9RD2 in 2005. In the experiment in well 34A-9, the co-injection earthquakes were more numerous, smaller, more explosive and had more horizontal motion, compared with the pre-injection earthquakes. In the experiment in well 34-9RD2 the relocated hypocenters reveal a well-defined planar structure, 700 m long and 600 m high in the depth range 0.8 to 1.4 km below sea level, striking N 20° E and dipping at 75° to the WNW. The moment tensors show that it corresponds to a mode I (opening) crack. Finally, for both wells, the perturbed stress state near the bottom of the well persisted for at least two months following the injection.
- Research Organization:
- Durham Univ. (United Kingdom)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Geothermal Technologies Office
- Contributing Organization:
- U.S. Geological Survey, Menlo Park, CA (United States); Naval Air Weapons Station, China Lake, CA (United States)
- DOE Contract Number:
- FG36-06GO16058
- OSTI ID:
- 926252
- Report Number(s):
- SGP-TR-185; TRN: US200818%%522
- Resource Relation:
- Conference: 33. Workshop on Geothermal Reservoir Engineering, Stanford, CA (United States), 28-30 Jan 2008
- Country of Publication:
- United States
- Language:
- English
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