| Title | Microseismicity at Groß Schönebeck - a Case Review |
|---|---|
| Authors | Luca Urpi |
| Year | 2011 |
| Conference | Stanford Geothermal Workshop |
| Keywords | microseismicity, reactivation, stimulation, stress field |
| Abstract | A cyclic hydraulic fracturing experiment has been performed to enhance the productivity of the geothermal research well at Groß Schönebeck (Germany) in 2007. During and after the stimulation treatment the recorded seismicity has been negligible compared to other similar hydraulic fracturing in crystalline rock. Towards the end of the treatment three small clusters of very low magnitude events (Mw max -1.0) have been located. The spatial distribution of hypocenters may indicate the reactivation of a small patch of a nearby fault: focal mechanism compatibility with shearing processes supports this interpretation, too. The authors investigated the causes of the delay in the occurring seismicity with respect to the beginning of the injection, modeling the variation in stress state by the aid of numerical model in a simplified environment and quantifying the increase in the probability of failure occurrence, through Hoek-Brown criterion. Water level data from the production well suggests limitations in the size of the fractured volume by a fault. Whether this is related to recorded seismicity or not has been analyzed. Microseismicity may be triggered by numerous causes. Changes in temperature and pressure distribution during stimulation treatment has been numerically modeled. The possible mechanisms behind the events recorded at Groß Schönebeck then has been reviewed, basing the analysis on their temporal and spatial distribution. |