Fig. 1

Overview of the study site. Panel (a) location of the geothermal field in the southern part of Munich city and projection on the surface of the trajectory of the six wells. Red lines denote production wells and blue lines show injection wells. The black dots show the location of the two nearest seismic monitoring stations, which are two borehole 3C-seismometers located to the East and to the Southwest of the SLS site. The Gauss-Kruger 4 coordinate system is used for the Northing and Easting markers. Panel (b) focus on the Schäftlarnstraße geothermal field. The gray polygon shows the location of the control room in which the Febus A1-R interrogator and recording system was installed on the well site. Panel (c) completion of the injection well TH3 along its first 900 m (top) and in the open-hole section, until final depth (bottom). The arrow highlights the flow direction. The TH3 FOC, which is the focus of the study, is cemented behind casing. The installation allows the section to be interrogated twice, since the FOC forms a U-loop with a micro-bend located at a depth of 692 m (TVD). The well is vertical in the section of interest. The FOC faces on one side a tieback filled with annulus fluid and on the other side, the shallow sedimentary layers of the Molasse basin. The column on the left shows the stratigraphy. Numbers 1 to 7 refer respectively to “Quaternary”, “Obere Süßwasser Molasse (OSM)”, “Süßbrackwasser Molasse (SBM)”, “Obere Meeresmolasse (OMM) Glaukonit Sande”, “OMM Blättermergel”, “OMM Neuhofener Schichten”, “Upper Jurassic (Malm) carbonate formation”. Panel (d) picture of the TH3 wellhead. The red rectangle highlights the entry point of the FOC in the ground, next to the location where the FOC was tapped to calibrate the position of the measuring points. Panel (e) picture of the setup in the control room. It shows the DAS interrogator, the Uninterrupted Power Supply (UPS) and the peripheral devices, which are all secured in a metallic enclosure