Numerical investigation of hydraulic stimulation strategies to mitigate post-injection seismicity in Enhanced Geothermal Systems

Enabling a widespread exploitation of Enhanced Geothermal Systems (EGS) around the world by tapping into the heat trapped by the radioactive granites demands a better understanding of the fluid-induced seismicity associated with their stimulation. Induced seismicity occurs not only during hydraulic stimulation, but also after shut-in. The induced earthquakes of Mw > 3 at Basel and Mw = 5.5 at Pohang are two well-known examples that have caused a negative public perception on EGS. Here, we numerically compare the effect of bleed-off on the mitigation of post-injection seismicity for three stimulation schemes: constant rate, step rate and cyclic injection. We find that applying bleed-off in the post-injection phase significantly reduces the post-injection induced seismicity when compared to not applying bleed-off in all the injection schemes.