Implementation and Evaluation of Distributed Acoustic Sensing (DAS) for Continuous Seismic Monitoring of Geothermal Fields in the Munich Area (Germany)

Supplying district heating networks with geothermal energy becomes a high priority to support the energy transition in areas prone to geothermal exploitation. The growth of this energy sector provides the industry with previously unavailable resources to implement advanced monitoring strategies, aiming to foster sustainable operation of the resource. In this context, local operators of the Munich area (Germany) are interested in the capabilities of the Distributed Fiber Optic Sensing (DFOS) for routine monitoring of the production and of the operated hydrothermal system – the porous Malm reservoir.
We share the outcomes and knowledge acquired from DAS measurements conducted over two years on two dedicated infrastructures in the Munich area. One consists of a 700 m long fiber optic cable (FOC), which is deployed in an injection well of the Schäftlarnstraße geothermal field. The second site consists of an 80-meter FOC section deployed in a loop configuration near surface and a dedicated well reaching a depth of 250 meters, complemented by a surface broadband seismometer. Our analysis encompasses a comprehensive range of monitoring tasks, starting from the handling of the substantial data flow using a dedicated data management system. ... mehrWe also explore its effective implementation as one additional component of the routine monitoring of the operational activity at the plant. The study covers different stages of data processing, from the data triggering and the detection of seismic events to the description of seismic sources, particularly in terms of location, moment magnitude, and stress drop. The presence of a co-located sensor allows for an assessment of the consistency of the DAS measurements. Moreover, the simultaneous deployment of a surface seismometer network and a low-aperture geophone array gives the opportunity to compare the capabilities of these different set-ups for detecting (micro-)seismic events within the study area.
The contribution of DAS to the monitoring network varies according to the location of the observed seismicity. However, our measurements show that DAS can complement the surface network by providing increased sensitivity for low-magnitude events close to downhole measurement points, and offers advanced processing capabilities, for applications beyond seismic monitoring too.