Electric Self-Potential Measurements during Fluid Injection at the Bedretto Underground Laboratory

Self-potential (SP) monitoring was implemented at the Bedretto Underground Laboratory as part of the BEACH experiment to complement multi-parameter observations during fluid-injection tests. Continuous SP measurements have been conducted since the end of October 2025, with data acquired so far covering the period until mid-December, and monitoring planned to continue throughout the current year.The SP setup consists of nine non-polarizable Pb/PbCl₂ electrodes installed along the tunnel wall and within one borehole in the Mesozoic Crystalline Fault Zone. Tunnel-wall electrodes were placed in shallow drill holes and embedded using conductive contact material to ensure stable long-term coupling to the rock. A single electrode was installed in a 50m borehole to provide additional depth sensitivity. All electrodes were connected to a CR6 data logger, recording continuous SP time series with a sampling interval of one value per minute.The recorded data span different operational phases, including background conditions as well as cold and warm water injection cycles and associated shut-in periods. This contribution presents an initial overview of the acquired SP dataset. Acknowledgements:BEACH – Energie Speicherung und Zirkulation von Geothermischer Energie in Bedretto receives funding from the Swiss Federal Office of Energy (SFOE), Project number SI/502817."Geo-INQUIRE is funded by the European Commission under project number 101058518 within the HORIZON-INFRA-2021-SERV-01 call."