著者

Fujii Yoshiaki Takahashi Kei Fukuda Daisuke Kodama Jun-ichi

出版者

Japanese Committee for Rock Mechanics

雑誌

Workshop on Rock Engineering and Environment proceedings(ARMS8)

巻号頁・発行日

vol.2014, pp.41-46, 2014-10-13

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An equation that represents the relationship between the volume of the injected water V and the maximum magnitude Mmax of induced earthquakes for various cases, including EGS (Enhanced Geothermal System), is expressed as M max = 0.75logV - 0.48 (1) Another equation that represents the relationship between the magnitude and the JMA (Japan Meteorological Agency) maximum seismic intensity scale SISmax of 40 randomly-selected, inland earthquakes in Japan is expressed as: SIS max = 1.36M - 1.12logd - 1.11 (2) where d is the focal depth (m). The equation that follows was derived from the preceding equations. SIS max = 1.02logV - 1.12logd - 1.76 (3) The volume of water injection by shale gas extraction in US was estimated and substituted into the equations, assuming that Eq. (2) could be used also for US earthquakes. The maximum magnitude and seismic intensity scale was predicted to be 6.0 and 3.5 (slight damage to residences), respectively, for the case where extraction had continued for 30 years. This estimate does not conflict with the fact that an M 5.6 event occurred five years after shale gas extraction began in the US. The same procedure was adopted for CCS (Carbon dioxide Capture and Storage) assuming that supercritical CO2 injection had the same effect in inducing seismicity. The injection volume is just 0.001% of the annual CO2 emission in Japan assuming that the allowable seismic intensity scale is 1. The injection of this small amount of CO2 is meaningless. We may have an M 7.1 whose SIS is 5.3 (heavy, significant damage to residences) if we inject 17% (this is IPCC's expectation) of the CO2 in Japan for 30 years into a CCS site. An M 7.1 is apparently not allowed. We need 510,000 CCS sites in Japan in order to inject 17% CO2 safely. It is impossible to construct so many CCS sites. In conclusion, either shale gas extraction or CCS should be carried out very carefully or we may have severe seismicity.