Seismic reflection and VSP in the kakkonda geothermal field, japan: fractured reservoir characterization

A seismic re~ection survey and a VSP "vertical seismic pro_ling# survey were conducted to obtain insight into the detailed characteristics of the fractured reservoir in the Kakkonda geothermal _eld\ Japan[ The geothermal reservoirs in this _eld are located in fractured Tertiary formations and a pre! Tertiary formation in contact with a younger Quaternary pluton[ The seismic survey technique with a very long o}!set distance proved to be e}ective at clearly imaging deeper re~ective events that correlate with the top of the deep pre! Tertiary basement[ Attenuation of the seismic signal "a very weakly re~ective or dim zone# has been found to be much greater in areas where major geothermal reservoirs have been identi_ed[ The weakly re~ective zone also corresponds to the concentration of microearthquake hypocenters[ We suggest that such weakly re~ective zones on the seismic re~ection section may be favorable drilling targets[ By combining the results of microeathquake monitoring "rate of occurrencemagnitude# with further case studies of seismic re~ection data of di}erent frac! tured reservoirs\ such a hypothesis can be tested[ The comprehensive seismic technique promises valuable insights into deep structures and fractured res! ervoirs for geothermal exploration[ 0887 CNR[ Published by Elsevier Science Ltd[ All ri`hts reserved[