Numerical simulation of fault slip during geothermal energy extraction

Enhanced geothermal systems (EGS) have been increasingly exploited as an alternative energy source. However, unexpected induced earthquakes bring uncertainty to their wider application. We employ a 2D thermal-hydro-mechanical (THM) coupled hybrid finite-discrete element method (FDEM) to investigate fault slip induced by injecting cold water into a hot fault under geothermal conditions. We show that slip will occur on stressed fault even if the overall stress condition is in the stable regime. This slip is caused by thermal contraction that reduces the fault normal stress locally, which also cause opening of the fault. We also found that convective heat transfer coefficient, which is typically unknown for natural faults, is a controlling factor for induced fault slip. This indicates the importance of understanding fault surface geometry.