Analysis of Injection-Induced Micro-Earthquakes in a Geothermal Steam Reservoir, The Geysers Geothermal Field, California
Conference
·
OSTI ID:934773
In this study we analyze relative contributions to the cause and mechanism of injection-induced micro-earthquakes (MEQs) at The Geysers geothermal field, California. We estimated the potential for inducing seismicity by coupled thermal-hydrological-mechanical analysis of the geothermal steam production and cold water injection to calculate changes in stress (in time and space) and investigated if those changes could induce a rock mechanical failure and associated MEQs. An important aspect of the analysis is the concept of a rock mass that is critically stressed for shear failure. This means that shear stress in the region is near the rock-mass frictional strength, and therefore very small perturbations of the stress field can trigger an MEQ. Our analysis shows that the most important cause for injection-induced MEQs at The Geysers is cooling and associated thermal-elastic shrinkage of the rock around the injected fluid that changes the stress state in such a way that mechanical failure and seismicity can be induced. Specifically, the cooling shrinkage results in unloading and associated loss of shear strength in critically shear-stressed fractures, which are then reactivated. Thus, our analysis shows that cooling-induced shear slip along fractures is the dominant mechanism of injection-induced MEQs at The Geysers.
- Research Organization:
- Ernest Orlando Lawrence Berkeley National Laboratory, Berkeley, CA (US)
- Sponsoring Organization:
- Earth Sciences Division
- DOE Contract Number:
- AC02-05CH11231
- OSTI ID:
- 934773
- Report Number(s):
- LBNL-468E
- Country of Publication:
- United States
- Language:
- English
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