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Estimate the Shear Wave Velocity Close to Wells from Tube Waves – An Experimental Study
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, Fourth Sustainable Earth Sciences Conference, Sep 2017, Volume 2017, p.1 - 5
Abstract
Within a VSP (vertical seismic profiling) acquisition, different wave types like P- and S-waves as well as tube waves are recorded. In general, mainly the direct arrivals of P- and S-waves are used for tomography studies, but the tube wave is also related to the shear modulus of the surrounding formation. If we could measure the velocity of the tube wave with high accuracy, it might be possible to estimate the shear velocity of the surrounding geological formation and possible changes. The advantage of this method is that no knowledge of the source position and firing time is required. However, the tube wave depends also on the parameters of the borehole and casing which has an impact on the sensitivity of the tube wave to the shear wave velocity. We conduct a VSP experiment in a 30 m deep borehole and extract the tube wave from most of the other arrivals. A simple modelling is performed for comparison with the measured data. We illustrate how accurate the tube wave velocity could be measured in our example and how the shear wave velocity of the formation could be estimated using existing theory.