An enhanced broad-frequency-band apparatus for dynamic measurement of elastic moduli and Poisson's ratio of rock samples.

Abstract

We built a broad-frequency-band measurement system for rock elastic parameters based on the stress-strain method following Batzle et al., Geophysics 71, N1-N9 (2006). The system gives strain amplitude anomalies at some measurement frequencies. These anomalies put limitations on the range of the measurement frequency and jeopardize the credibility of the measurement results over a broad frequency band. To overcome these limitations, we investigated the cause of these anomalous strains by numerical model simulations with a finite element method based on the experimental apparatus. Through the systematic analysis of the modeling results, we conclude that the resonances caused by non-axial perturbations lead to such anomalous measurement results. Based on the analysis, we give a solution to reduce the effect of the resonances and shift the first resonance frequency beyond the frequency band of 1-2000 Hz. The enhanced measurement system can provide robust and reliable measurements on the elastic parameters of rocks between 1 and 2000 Hz, which is crucial for a quantitative study of the frequency-dependent phenomenon related to fluid effects. This in turn will provide a powerful tool for the experimental characterization of elastic properties of oil/gas reservoir rocks, thus laying a solid foundation for low-frequency rock physics analysis and quantitative seismic interpretation.