Thermo-Hydro-Mechanically coupled stress propagation and its possible effects on induced seismicity

The inducement of earthquake has been usually thought to be a result of coupled behaviors of fluid and solid mechanics. On the other hand, recent studies have started to focus on the contribution of thermal stress. In the enhancing geothermal energy systems (EGS) popularizing today, it seems to be very necessary to study the earthquake inducements considering thermo-hydraulic-mechanical coupling behavior. Especially, EGS engineering project failure in Pohang and Basel showed that large magnitude earthquakes may be induced during hydraulic fracturing process during geothermal energy extraction from enhanced geothermal systems.

In order to ascertain the relationship between thermal stress and seismicity, a coupled thermal-hydro-mechanical (THM) scheme is formulated by using the finite element method to investigate the inducements of seismicity during geothermal heat injection. Current results with a schematic model suggested that the thermally induced strain might propagate 100 times slower than hydraulically induced strain in an injection process, and then, the possibility of later seismicity caused by the slower propagation of the thermal stress.