Keywords:Geological CO2 Storage, Fiber Optic Sensing, Seismicity
Geological CO2 storage requires long-term monitoring not only for a plume of injected CO2 but also area of pressure/strain propagation far away from the plume. The Distributed Fiber Optic Sensing (DFOS) is one of the major technologies capable of acquiring spatially continuous recording. The optical fibers for vibration sensing are used as receivers for the 4D VSP (Vertical Seismic Profiles) techniques in order to image the plume of injected CO2, and also as passive seismometers for natural/induced seismicity. The sensitivity of optical fibers is not as good as typical geophones/seismometers. We conducted the long-term observation for natural earthquakes using the strain-sensing fiber cables installed behind the casing along the vertical wellbore in order to evaluate the sensitivity of the fiber cables.
A single channel record of the fiber optical sensing captured the ground motion of relatively large earthquake events. Whereas, the earthquake events within 20 km epi-distance listed on the JMA website location were all detected using the fiber records along the 880m well. Considering to the area of monitoring in the geological CO2 storage (~10km), the fiber optic vibration sensing is one of the feasible options for seismicity monitoring.