The acoustic reflectivity and transmissivity of liquid saturated porous media: Experimental tests of theoretical concepts

Acoustic wave propagation, reflectivity and transmissibility in porous media are presented. A new experimental method of probing various materials was developed. It utilizes a large ultrasonic source and a near-point receiver. The effects of geometrical spreading and averaging at the point of observation are minimized.; The calibration of the method on elastic materials immersed in water revealed a large amplitude drop at the so-called Rayleigh angle of incidence. Extensive modelling has shown that the phase of the reflection coefficient is solely responsible for this energy drop and the apparent shift of the wave-field is attributed to a “spatial dispersion effect” and not a leaky Rayleigh wave in the solid as previously suggested in the literature. This was supported by experimental measurements. The method was sufficiently understood to be used in more complex materials.; In addition to the compressional and shear wave modes, a transmission experiment conducted on a thin water-saturated porous plate definitively detected the highly attenuated slow P-wave. Further, an additional mode that may be the porosity wave was observed. Further modelling is necessary to confirm this fourth wave. Measured velocities and attenuations of the transmitted waves are in agreement with the theory. Further, the reflectivity experiment revealed conversions of both P and S-waves to slow P-waves. To the author's knowledge, this is the first reported observation of such conversion modes in a reflectivity experiment.; Reflectivity curves were acquired from water-saturated thick porous plates immersed in water. These plates exhibit a low degree of sintering and large thickness, and consequently large “dry” P and S-attenuations and not all required parameters could acceptably be obtained. A numerical approach is employed instead yielding satisfactory reflectivity results. However, some features were not modelled properly.; Both the Biot and the de la Cruz/Spanos theories were reviewed, employed in the modelling, and compared in the context of the present experiments. When water is considered both theories adequately explained the observations but similarities break down for higher viscosity fluids.; Zoeppritz's equations are found to disagree with the observations at ultrasonic frequencies. Extrapolation to seismic frequencies is left to future work.