Initial Results from the Field on the Use of DAS as a Viable Microseismic Monitoring System of CCS Sites

In outdoor field-tests where a single optical fibre cable is used to make DAS recordings of hammer shots, coherent seismic arrivals are observed at up to 32 m from the hammer points with frequencies up to 600 Hz. Recording at higher sampling rates and decimating is preferable to downsampled data. Time domain SNRs of acquired DAS data at a given distance are ~1/2 those of complimentary geophones while in the frequency domain, the highest ratios are produced between 20 and 200 Hz. An automated STA/LTA trigger algorithm is able to define reasonable seismic onsets but is unable to identify the first-arriving energy on all traces. Shorter pulse widths produce lower RMS amplitudes for the noise windows while longer pulse widths produce higher RMS amplitudes for the signal windows. This means that the selection of optimum pulse width with respect to maximising the SNR is not clear. This work presents the initial results of field-tests that will be used to refine the use of the DAS system in further field and borehole experiments. This will ultimately be used to monitor the seismicity at active CCS injection sites in the future.