Accuracy analysis of ultrasound shear-wave velocity measurement of rock plug sample
Wei Jianxin1,2,3, Di Bangrang1,2,3
1. State Key Laboratory of Petroleum Resource and Prospecting,Beijing 102249,China;
2. CNPC Key Physical Exploration Laboratory,Beijing 102249,China;
3. College of Geophysics and Information Engineering,China University of Petroleum
Abstract：Most laboratory measurements of shear-wave velocity of rocks are conducted on plug samples with small diameters.The accuracy of velocity measurement of shear-waves in different vibration modes can be affected by the diameter and frequency of the transducer.By measuring the shear-wave velocity of four homogeneous materiass and litho-logically different rock samples using shear and torsional transducers at two different frequencies, the authors find that an associated wave appears before the shear-wave, inversing the phase of the latter and shifting it forward, which will affect the arrival-time picking of the shear-wave.Meanwhile, the torsional transducer will produce reflections at the side interface, which will further decrease the accuracy of measurement.By analyzing and comparing the measurements on rock samples with different diameters and lithology, a method is proposed to correctly estimate the phase and time of shear-wave arrivals.This method improves the accuracy of shear-wave velocity measurements on plug rock samples.
