Hydromechanical characterization of a fractured crystalline rock volume during multi-stage hydraulic stimulations at the BedrettoLab

Multi-stage hydraulic stimulation experiments were conducted at the Bedretto Geothermal Testbed (Switzerland) at a depth of over 1 km to study seismo-hydromechanical processes at the hectometer scale. Eight intervals with a total length of 206 m were stimulated within a densely monitored, fractured granitic rock volume. Geological characterization shows that all intervals contain NE-SW striking, steeply dipping fractures, but the transmissivity and natural inflow vary between intervals. Reactivation pressures estimated from injectivity increases during stimulation indicate shear reactivation rather than hydraulic jacking, suggesting reactivation of pre-existing non-filled fractures. Overall, the seismo-hydromechanical response to stimulation is heterogeneous and indicates channelized flow. • Multi-stage hydraulic stimulations performed in a fractured crystalline rock volume. • Novel hectometer-scale at >1km depth reveals heterogeneous rock mass response. • Stimulation intervals contain steeply dipping NE-SW striking non-filled fractures. • Most stimulations cause a strong injectivity increase at comparable pressures. • Reactivation pressures can be explained by shearing of pre-existing fractures.