| Title | Estimation of Radiational Mechanism of AE Multiplets Observed While Hydraulic Fracturing in HDR Reservoir |
|---|---|
| Authors | Yusuke Kumano, Hirokazu Moriya, Hiroaki Niitsuma |
| Year | 2005 |
| Conference | World Geothermal Congress |
| Keywords | Induced AE multiplet, Waveform similarity, Streaks of source distribution on multiplet plane, Direction of shearing stress, Asperity |
| Abstract | Multiplet is a group that consists of seismic events with similar waveforms, and observed in a variety fields, e.g. oil or geothermal reservoir or natural seismicity. In this paper we deal with induced microseismic (AE) multiplets observed during hydraulic fracturing at Soultz-sous-ForÍts HDR field, France in 1993. The multiplet analysis has been one of mapping techniques, using cross- spectrum analysis. We noticed the similarity of the microseismic waveform and observed waveforms of microseismic events in detail. During observations we found that the similarity was not related to the amplitude of microseismicity, and the similarity of waveforms varied with matching of events. All the events included in one multiplet group showed similar waveforms at P-wave arrival. Waveforms of some events included in one multiplet group fit together almost perfectly, as well as those of coda wave and P-wave arrival part. It is reported in conventional multiplet analysis that source locations of microseismic multiplet events revealed the structural plane (multiplet plane). On a multiplet plane we divided the multiplet events by similarity of waveforms. Then we found streaks consisting of multiplet events with especially similar waveforms, on the multiplet plane. The directions of streaks were uniform in one multiplet plane and not consistent with the calculated maximum shearing stress direction on the plane, indicating that the microseismic multiplet streaks were not related to the slip direction of the fracture. |