Characterization of Fracture Patterns in the Geysers Geothermal Reservoir by Shear-wave Splitting
The authors have analyzed the splitting of shear waves from microearthquakes recorded by a 16-station three-component seismic network at the Northwest Geysers geothermal field, Geysers, California, to determine the preferred orientation of subsurface fractures and cracks. Average polarization crack directions with standard deviation were computed for each station. Also, graphical fracture characterizations in the form of equal-area projections and rose diagrams were created to depict the results. The main crack orientations within the steam field are predominantly in the N10{degree}E to N50{degree}E direction, consistent with expected fracture directions in a pull-apart basin created by sub-parallel right-lateral strike-slip faults related to the San Andreas fault system. Time delays range from 15--60 ms, similar to the time delays from previous studies at geothermal reservoirs. They have detected a significant increase in time delays between 1988 and 1994, which they attribute to widening of the cracks or filling of the cracks with fluid. Increase in production activities during this time also could have influenced this widening.
- Research Organization:
- USDOE Idaho Operations Office, Idaho Falls, ID; University of North Carolina, Chapel Hill, NC (US)
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EE) (US)
- DOE Contract Number:
- FG07-96ID13468
- OSTI ID:
- 758724
- Report Number(s):
- DOE/ID/13468; TRN: AH200028%%91
- Resource Relation:
- Other Information: PBD: 15 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography. [Quarterly progress report 03/16/1998 - 06/15/1998]
A comprehensive study of fracture patterns and densities in the Geysers geothermal reservoir using microearthquake shear-wave splitting tomography [Quarterly progress report 06/16/1998 - 09/15/1998]