Propagation of Transient Acoustic Waves in Porous Media

摘要

Acoustic waves are standard diagnostic tools in determining the mechanical parameters (volume density of mass, compressibility, elastic stiffness) of fluids and solids. Ideal fluids and isotropic solids carry compressional waves, while, in addition, isotropic solids sustain shear waves. So the detection of a shear wave is indicative that the medium through which the waves propagate is a solid. As soon as the solid becomes porous and the pores are completely filled with an ideal fluid, an extra (slow) compressional wave occurs in case the pore sizes are small compared to the wavelength. So the existence of a slow compressional wave is indicative that the solid is a porous one. A computational model study can possibly reveal, whether or not, and under which circumstances, such a slow compressional wave can be detected in a seismogram. The next question is how the properties of the slow compressional wave correspond quantitatively to the volume fraction and other geometrical properties of the pores. For this, insight is needed in the relationship between microscopic geometrical and macroscopic acoustic properties of porous solids, rock, for example. With this in mind, the authors investigate the scope of a macroscopic linear acoustic theory for impulsive wave propagation in a porous medium.