Background

The understanding of the coupled thermo-hydro-mechanical behavior of fault zones in naturally fractured rocks is essential both for fundamental and applied sciences and for the safety assessment of radioactive waste disposal facilities. An international research program called CHENILLE was built to address key questions related to the impact of high temperatures (up to 120°C) on shear zones as well as fault reactivation processes in shale formations. We report on thermally controlled in-situ fluid injection experiment on a strike-slip fault zone outcropping at Tournemire Underground Research Laboratory, Southern France. Another challenge during the development of EGS by hydraulic stimulation we face the challenge to increase permeability and mitigate the risk of large magnitude injection-induced seismic events. One main parameter is the injection protocol. Injection parameters include pressurization rate, depressurization at the end of injection, flow rate, cyclic injection protocols and hydraulic and seismic energy. Overall, we find that the injection protocol can influence the stimulation results to a certain degree. However, site-specific geology and pre-existing fracture networks, require extra attention for tailor-made injection strategies.

Scientific key questions

• What are the critical parameters to make a fault slip?
• How can we increase fault permeabilty and control induced seismicity?
• Which role do fatigue processes play in unlocking deep heat for a clean energy future?

Related projects

• CHENILLE | Cross-scale process understanding of malfunctions from laboratory to field scale