On excitation efficiency of the fast and slow biot waves in water and gas saturated media

The theoretical analysis of the acoustic waves characteristics is carried out in application to the study of the problem of elastic wave propagation through fluid and gas saturated porous media with the use of some artificial Biot models. Phase velocity dispersion and absorption coefficient frequency dependence of the fast and slow P-waves are calculated on the base of Biot theory describing the wave propagation in two-component medium. The influence of the exchange of water by air component on the wave velocity and on the wave attenuation by the same skeleton characteristics of the medium is an important part of the investigation. The numerical calculation of the P-1, P-2 total radiation wave power as the frequency function is made in appliance to the pulsation pressure source, which works in infinite porous medium saturated by water or by air and excites the fast and slow compression waves. The fluid component exchange (water by air) is provided by the specific choice of the dimensionless Biot parameters. It is shown that there is the energy domination of P-1 waves, which propagate far from the pressure source through the porous saturated medium in the case of both types of its fluid components. The wave powers of the fast and slow waves radiated by source are almost the same in the water saturated medium but P-2 wave attenuation is much greater and as a result only P-1 wave remains in around space. In contrast to this there is infinitesimal attenuation of both waves which propagate in the air saturated medium but P-1 wave power radiated by the source is significantly greater that leads to the domination of the fast compression wave in this case as well. This result is valid under the condition of equal pulsation volume velocities of the source, which act on skeleton and on fluid medium components simultaneously. Elastic waves of vibration sources that work in boreholes at the depths where medium has a higher fluid saturation degree will differ by their characteristics from the similar sources working near layers with air saturation medium. This difference can be considered as a sign of the fluid saturation degree that can be measured experimentally.