Seismic Calibration of Distributed Acoustic Sensors (DAS) in a Joint Borehole-surface Experiment

Distributed acoustic sensors (DAS) are an emerging fibre optic-based technology enabling seismic investigations with innovative configurations by massive receiver arrays in boreholes and at the surface. Advantages of DAS technology include lower equipment costs and reduced installation complexity, especially in boreholes, with respect to equivalent applications using conventional seismic sensors. We present results of a joint borehole-surface calibration experiment. The main targets of this study were the analysis of S/N and of the directional responses for recorded wavefields. Borehole signals were acquired by DAS and compared with signals acquired by permanent 3C geophones installed outside the casing of the instrumented well at maximum depth of about 200 m. Multi-offset vertical seismic profiles were acquired by a surface seismic vibrator source with two different azimuths. At the surface, settings of buried and near-surface sensors was prepared in a cross of trenches using DAS cables along with single and multicomponent geophones at corresponding positions. Using the surface installation, a reciprocal seismic line was acquired by maximum offset of approximately one kilometer for the vibrator source. The analysis shows the correspondences in the seismic wavefields acquired by the different methods, compares the physical quantities, and confirms the quality of the DAS signals.