[MTT50-05] A Field Test in Preparation for Long-Range Distributed Acoustic Sensing in Subsea Applications
Keywords:Distributed Fiber-optic Sensing, Seismic, Subsea
Due to having many active or passive optical components subsea installations are often non-optimal for sensing purposes. A series of built-in losses at connectors, splices, penetrators, as well as other optical components, leads to typical light propagation loss-budgets of 8-11 dB. For seismological applications these budgets are suitable for the larger gauge lengths due to the lower frequency waves of interest. However, for higher frequency applications, smaller gauge lengths and pulse widths are required, while still overcoming the light propagation losses
To demonstrate that we can properly interrogate, we acquired field test data on-shore utilizing boreholes and surface layouts with a 5 km section of fiber after a 30 km lossy lead-ins, which is a typical scenario for industrial seismic applications. The data acquisition utilized standard telecom and borehole fiber cables permanently deployed at an on-shore field site. A low-energy vibrator with sweep frequencies from 8-150 Hz was used. High SNR seismic wave fields containing direct arrivals, refractions and reflections in all active sensing sections. The results show that state-of-the-art DAS interrogators can be used efficiently in a practical field setting for various subsea sensing applications. Future applications include long-reach subsea surface and borehole-based sensing for seismic imaging purposes, and opportunistic interrogation of active or abandoned boreholes.