Spatial distribution of coherent microseismic events at Cooper Basin, Australia

In previous work (Kumano et al., 2003, Asanuma et al., 2004), we analyzed the AE data set obtained at Cooper Basin Hot Fractured Rock (HFR) geothermal field, Australia, during hydraulic stimulation conducted in the last quarter of 2003. Source locations of microseismic events were determined using a standard earthquake location procedure, SED. Location uncertainties were found to be as great as the thickness of the seismic cloud, however, thus preventing us from making meaningful interpretations regarding details of the fracture system within reservoir. We applied microseismic multiplet analysis to improve relative source location accuracy. This method can illuminate the detailed fracture system and physical phenomena associated with microseismicity by characterizing the waveform similarity of microseismic events. We then relocated the events using a Double-Differential source location technique, and imaged the reservoir structure using the spatial distribution of coherent microseismic events. The adjusted source distribution suggests that the reservoir fracture system consists of sub-parallel planar structures, and the spatial distribution of coherent microseismic events indicates that these sub-parallel structures each comprise a simple fracture system that is independent from the others.