%0 Journal Article
%@ 0037-1106
%A Baisch, Stefan
%A Weidler, R.
%A Vörös, Robert
%A Wyborn, D.
%A de Graaf, L.
%A Q-con GmbH Marktstr. 39 76887 Bad Bergzabern, Germany,
%A Geodynamics Limited 11 Lang Parade, Milton Queensland 4064, Australia,
%D 2006
%F epos:1375
%I Seismological Society of America
%J Bulletin of the Seismological Society of America
%N 6
%P 2242-2256
%T Induced Seismicity during the Stimulation of a Geothermal HFR Reservoir in the Cooper Basin, Australia
%U https://episodesplatform.eu/eprints/1375/
%V 96
%X A long-term fluid-injection experiment was performed in the Cooper  Basin (Australia) in 2003 to stimulate a geothermal reservoir. More than 20,000 m^3  of water were injected into the granitic crust at 4250 m depth. During reservoir  stimulation about 27,000 induced seismic events were detected by a local, eight-station seismic monitoring system deployed in nearby boreholes. Hypocenter loca-  tions for 11,068 events were determined by using an averaged velocity model that  was calibrated by associating early events with the injection point. The spatial hypocenter distribution forms a nearly subhorizontal structure with a lateral extension  of 2 km x 1.5 km and an apparent thickness of approximately 150–200 m, which  is in the order of the hypocenter location confidence limits. The hypocenter distribution exhibits a high degree of spatiotemporal ordering with the seismic activity  systematically migrating away from the injection well with increasing time. Previously activated regions become seismically quiet indicating relaxation processes.  High-resolution relative hypocenter locations determined for clusters of “similar”  events locally reduce the apparent thickness of the structure to the level of a few tens  of meters indicating that the reservoir is dominated by a single fracture zone only.  Consistent with these findings, a subsequently drilled well intersects a dominating,  high-permeable fracture within 15 m of the predicted intersection depth. Based on  drilling and logging information, the fracture zone is interpreted as a preexisting  (possibly tectonically formed) feature that (partly) sheared during stimulation. Triggering of the induced seismicity is found to be predominantly controlled by the  increase of fluid pressure implicating a (local) reduction of the effective normal stress  resolved on the fracture plane. Additionally, perturbations of the stress field caused  by the largest-magnitude events may trigger seismicity (“aftershocks”) on a local,  short-ranging scale.