Seismic monitoring of geothermal reservoirs using Distributed Acoustic Sensing on dark fibers: the RUBADO project

Applied to existing but underutilized fiber-optic networks (dark fibers), Distributed Acoustic Sensing (DAS) offers an attractive approach for large-scale seismic monitoring with minimal deployment effort. However, the approach introduces specific challenges, as existing infrastructures were not designed for this purpose, leading to constraints related to sensor coupling, heterogeneous installation conditions, and limited characterization of the measurement points. In the frame of the RUBADO project, we investigate the potential and limitations of DAS applied to dark fibers to provide seismic observations supporting both operational monitoring and characterization of deep geothermal reservoirs. The approach is implemented at multiple spatial scales within the Upper Rhine Graben, where several geothermal plants are currently operating, under development, or in the planning phase. In this context, research activities within the project specifically target key practical challenges related to the use of DAS on dark-fibers for the seismic monitoring of geothermal reservoirs. Currently, data are recorded along a ~20 km fiber-optic line using the KIT infrastructure, which will support the monitoring of the drilling of a 1.4 km-deep geothermal well at KIT Campus North. We present early results from local and regional seismic monitoring and associated methodological approaches for signal enhancement and seismic event detection. We also introduce a framework for subsurface characterization that leverages the frequent vehicle-generated signals observed in the DAS recordings. We then outline planned measurements at the scale of the Upper Rhine Graben, where a key feature is the simultaneous use of multiple dark-fiber lines. Given the geometry of the planned dark-fiber network, DAS observations will enable the simultaneous monitoring of several geothermal sites with favorable spatial coverage.