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Post shut‐in seismic events in enhanced geothermal systems (EGSs) occur predominantly at the outer rim of the co‐injection seismic cloud. The concept of postinjection fracture and fault closure near the injection well has been proposed and validated as a mechanism for enhancing post shut‐in pressure diffusion that promotes seismic hazard. This phenomenon is primarily attributed to the poro‐elastic closure of fractures resulting from the reduction of wellbore pressure after injection termination. However, the thermal effects in EGSs, mainly including heat transfer and thermal stress, may not be trivial and their role in postinjection fault closure and pressure evolution needs to be explored. In this study, we performed numerical simulations to analyze the relative importance of poro‐elasticity, heat transfer, and thermo‐elasticity in promoting postinjection fault closure and pressure diffusion. The numerical model was first validated against analytical solutions in terms of fluid pressure diffusion and against heated flow‐through experiments in terms of thermal processes. We then quantified and distinguished the contribution of each individual mechanism by comparing four different shut‐in scenarios simulated under different coupled conditions. Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity, and suggest that heat transfer can further augment the fault closure‐induced pressure increase and thus potentially intensify the postinjection seismic hazard, with minimal contribution from thermo‐elasticity. We used numerical simulations to investigate the impact of thermal effects on fluid diffusion after injection and to provide insights into the thermal effects on postinjection seismicity in enhanced geothermal systems. Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity. Heat transfer can further promote the fault closure‐induced pressure increase and potentially intensify the postinjection seismic hazard, with negligible contribution from thermo‐elasticity. We used numerical simulations to investigate the impact of thermal effects on fluid diffusion after injection and to provide insights into the thermal effects on postinjection seismicity in enhanced geothermal systems.Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity.Heat transfer can further promote the fault closure‐induced pressure increase and potentially intensify the postinjection seismic hazard, with negligible contribution from thermo‐elasticity. We used numerical simulations to investigate the impact of thermal effects on fluid diffusion after injection and to provide insights into the thermal effects on postinjection seismicity in enhanced geothermal systems. Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity. Heat transfer can further promote the fault closure‐induced pressure increase and potentially intensify the postinjection seismic hazard, with negligible contribution from thermo‐elasticity.

Abstract: The technical feasibility of geothermal power production in a low enthalpy environment will be investigated in the geothermal site at Groß Schönebeck, North German Basin, where a borehole doublet was completed in 2007. In order to complete the Enhanced Geothermal System, three massive hydraulic stimulations were performed. A seismic network was deployed including a single 3-component downhole seismic sensor at only 500 m distance to the injection point. Injection rates reached up to 9 m3/min and the maximum injection well-head pressure was as high as ∼60 MPa. A total of 80 very small (−1.8 < M W < −1.0) induced seismic events were detected. The hypocenters were determined for 29 events. The events show a strong spatial and temporal clustering and a maximum seismicity rate of 22 events per day. Spectral parameters were estimated from the downhole seismometer and related to those from other types of induced seismicity. The majority of events occurred towards the end of stimulation phases indicating a similar behavior as observed at similar treatments in crystalline environments but in our case at a smaller level of seismic activity and at lower magnitudes.

Lithiumsalze der 1-Alkoxy-1-buten-3-ine lassen sich mit Säureanhydriden in guter Ausbeute zu 1-Alkoxy-1-alken-3-in-5-onen (1) acylieren, die durch alkalisch katalysierte Methanoladdition in Carbonylderivate von 3,5-Diketoaldehyden übergehen.