Characterization, hydraulic stimulation, and fluid circulation experiments in the Bedretto Underground Laboratory for Geosciences and Geoenergies

Reservoir stimulation and hydraulic fracturing in oil-and-gas reservoirs has become common practice and the techniques are continuously improved. However, directly applying the same techniques to extract geothermal energy from low permeability crystalline rocks (i.e., Enhanced Geothermal Systems, EGS) continues to present operational challenges. The research community and industry have shown great interest in addressing the unresolved problems using down-scaled in-situ hydraulic stimulation experiments. Focus has been on the 1-10 m field scale, but in comparison to a realistic EGS operations (1000s m) the scale is two orders too small, the depth and associate stress field differ, and the hydraulic conditions are not perfectly representative. To study the processes in-situ and to bridge the scale between in-situ labs and actual EGS projects, the Bedretto Underground Laboratory for Geosciences and Geoenergies (BULGG) was built in a tunnel in the Swiss Alps so that hydraulic stimulation experiments could be performed with dense monitoring systems at the 100 m scale. This effort enables process-oriented research and testing of field scale techniques at conditions that are closer to target reservoir depths and scale. This study gives in-sight on the initial geologic, hydraulic, and stress characterization of the BULGG related to on-going stimulation and circulation experiments.