Distributed Acoustic Sensing (DAS) passive seismic monitoring of a geothermal field with linear and helically-wound fiber

Although geothermal energy is often thought of as providing a clean source of renewable energy, in fact, most geothermal energy plants emit CO2 and small amounts of other gases, typically up to 5% of by weight. At the Hellisheidi geothermal field in Iceland, produced geothermal fluids and CO2 are captured and reinjected via multiple wells. It is vital to understand the possibilities and limitations of injection through geophysical monitoring of the effects. In this study an analysis of fibre-optic Distributed Acoustic Sensing (DAS) passive seismic data is made to assess the suitability of different cable designs (linear and helically wound (HWC) fibre-optic cable) to record any local induced seismicity and regional natural seismicity. Local seismicity with magnitudes (M) as low as M=0 is detected on both the linear and HWC parts of the trenched surface array. Recordings of regional seismic events show higher signal-to-noise recordings of surface waves and S-waves on the linear cable, as predicted by theory.