Shear-wave polarizations in a hot dry rock geothermal reservoir: Anisotropic effects of fractures

摘要: Abstract Hydraulic fracturing at the Hot Dry Rock Geothermal Project in Cornwall stimulated extensive cracking Carnenellis granite. The acoustic emissions were monitored by a surface network of three-component seismometers which recorded events with double-couple mechanisms indicating release significant shear stress. Three-component wavetrains display splitting diagnostic crack-induced anisotropy. Equal-area projections shear-wave polarizations patterns characteristic propagation through parallel vertical liquid-filled microcracks, where orientations leading arrivals are to strike cracks. This is confirmed elongated distribution events, and indicates stress direction depth fractures. approximately one sets joints si 20° away from axis compression measured about 10km northwest HDR site. consistency before after water injection that intact granite rock mass 2 km has anistropic symmetries uncharged hydraulic fracturing. demonstrates presence stress-aligned microcracks (extensive-dilatancy anistropy, EDA) as most rocks cool brittle upper 10–20 crust. There two main applications demonstrated this case study. 1. (1) orientation features can be predicted waves injection. direct way do would record vibrators seismic profiles, suggested Crampin [1] 2. (2) correlation between wave polarizations, existence EDA orientations, preferred directions flow contain important information internal geometry cracked reservoir rock. Again, access VSPs.