Study on Dispersion of Longitudinal Elastic Waves in Porous Media
Satoshi NISHIYAMA, Takao YANO and Yuzo OHNISHI
Abstract:Survey methods using elastic wave velocity have been performed in order to estimate the pore fluid properties in rock mass, but the viscosity and density of pore fluid have not been estimated quantitatively by the values of velocity or the velocity changes. We describe in this paper whether pore fluid properties can be estimated by using the dispersion of longitudinal elastic waves. We measured the frequency-dependent velocity data of longitudinal elastic waves in porous specimens and the dependence of the velocity dispersion on the kinematic viscosity of pore fluid. Moreover, we try to explain the velocity dispersion shown by the measurement data using the Biot theory. The Biot theory explains that the dispersion phenomenon is caused by the elastic property change in the media with the interaction between the solid phase and liquid phase, so the dispersion is dependent on the properties of liquid phase. The measurement data showed the phase velocities of longitudinal waves increased with an increase of frequencies and the characteristic frequencies which indicate the points of inflection moved to higher frequencies with an increase of kinematic viscosities of pore fluid. We report that we can estimate the kinematic viscosity of pore fluid in rock mass by using the dispersion curves which graphed the relation between the phase velocities and frequencies. Key Words:Dispersion, Kinematic viscosity, Longitudinal elastic wave, Biot theory, Pore fluid