Ultrasonic P Wave Velocity Measurement of Sedimentary Rocks in Laboratory and Its Dependency on Different Parameters by Using Multivariate Regression Analysis

Ultrasonic Pulse Velocity (UPV) is one of the non-destructive geophysical method commonly used in different fields such as civil, mining, geotechnical, and rock engineering. Ultrasonic technique is generally used to reproduce seismic waves in the laboratory. By doing so, different petrophysical and mechanical properties of rocks can be investigated by correlating it with the ultrasonic velocity. However, the range of frequency of the ultrasonic technique, to be used in laboratory or field, may also influence the velocity measurement, although it is not yet highlighted in the literature. The standards (ASTM/ISRM codes) only stipulate that as long as the wavelength is significantly greater than the grain size, the velocity values determined do not appear to be frequency dependent. In order to explore the influence of frequency, UPV measurements were conducted at 54 and 500 kHz frequency on dry rock cores of varying dimensions at ambient conditions in the laboratory. It was observed that 500 kHz transducers gave higher velocity measurement values than 54 kHz transducers. UPV54kHz and UPV500kHz were correlated using regression analysis, and R2 obtained was 0.76. Moreover, a method based on multivariate analysis was developed to determine the influence of different parameters, namely diameter, length, aspect ratio, bulk density of sedimentary rocks on UPV measurements, and subsequently, R2 increased to 0.91.