Calculation of Tube Wave Velocity in a Shallow Borehole Using Passive Seismic Recordings

With the initial goal of measuring the noise levels in our laboratory, we used an array of hydrophones to record around 11h of seismic data in a 95m-deep, water-filled well. No active seismic source was employed. During data processing, a coherent event was detected, and interpreted as a tube wave.

The velocity of this event was calculated using two independent methods, with the results showing consistency with each other and over time. We believe this could be a way to continuously measure the tube wave velocities in wells, without the need of an active seismic source. Since the tube wave velocity is a function of the shear modulus of the formation behind the casing, this can be also used as a monitoring tool.