Numerical Study on the Induced Seismicity Through Hydraulic Fracturing in the Deep Heat Mining Project in Basel, Switzerland Using a Pseudo Dynamic Model and Considering Fully Hydro-Mechanical Coupling

The induced seismicity associated with fluid injection (hydraulic fracturing) or forced circulation has become a key issue in the safe exploitation of hot dry rock geothermal energy. In this paper, the induced seismicity in the Deep Heat Mining Project in Basel, Switzerland was numerically studied by using a developed 3D numerical code with considering the fully hydro-mechanical coupling and the dynamic stress transfer effects. The numerical study was based on history matching of the injection pressure and the statistic characteristics of the induced seismicity. Further, sensitivity analysis of some parameters relating to injection operation, slip behavior and strength-stress ratio was conducted. According to this study, the following conclusions were obtained: 1) the temporal and spatial distribution of the seismic events can be divided into an indirectly induced zone, a directly induced zone, and a quiet zone; 2) large seismic events can be found within the indirectly induced zone; 3) the released energy is not exactly proportional to the injection volume; 4) when the geological condition is well-known, the maximum induced seismicity by fluid injection can be approximately determined; 5) the slip behavior and the strength-stress state are dominate factors for inducing large seismic events.