| Abstract |
Induced seismicity risk is a topic that has been addressed on numerous occasions since 2004 by collaborating countries within the IEA (International Energy Agency) Geothermal Technology Collaboration Programme (TCP) Working Groups (most recently under WG13, Task D). It remains an issue for geothermal projects, worldwide, particularly those involving deep EGS fracture stimulations, and those located near fragile buildings or in densely-populated regions where people are not used to natural earthquakes. The initial induced seismicity Working Group focus was on developing a protocol to assist developers and regulators, as well as providing a forum for research collaboration and information exchange. Efforts also focussed on establishing consistent data protocols, understanding mechanisms, and improving advanced forecasting methods. Such methods may use a modified traffic-light approach for adaptive response to observed levels of seismicity, by modifying injection and stimulation parameters. A further objective was to better understand, through collaborative modelling and data sharing, the key mechanisms behind induced seismicity that can sometimes accompany long term injection. In conventional operating geothermal fields, typically hosted in fractured hydrothermal systems and in tectonically stressed regions, monitoring of micro-seismicity provides geothermal reservoir modelers and resource managers with improved information on geothermal reservoir behaviour and extent. This information complements other geophysical monitoring tools, enabling production and reinjection strategies to be fine-tuned to improve utilization sustainability. The knowledge gained can also help develop better strategies for resource expansion and for choosing targets for make-up drilling. In the spirit of IEA-Geothermal collaboration, this paper shares examples of such reservoir management benefits from seismically active volcanic zones, including the Taupo Volcanic Zone of New Zealand. Numerous induced events have been documented, typically several per year in the magnitude range of 3 to 4. So far, there have been no cases of significant damage, and perhaps consequently, no public opposition to ongoing geothermal development. In New Zealand, all felt event information (above magnitude 2), whether induced or natural, are almost immediately available online (www.geonet.co.nz). This openness appears to provide the public with a sense of reassurance. |