Low-Frequency Stoneley Wave in Poroelastic Waveguides

Phase velocity and attenuation of generalized Stoneley wave being a symmetric trapped mode propagating along a thin poroelastic layer embedded into a poroelastic medium are studied. Porous media are treated within Biot theory. Full dispersion relation is derived. A biquadratic equation for wavenumber is found that gives analytical approximation of the exact solution provided a set of reasonable assumptions is satisfied. In the frequency range of 0.01−1000 Hz and for layer width less than 10 cm, the quality of the analytical approximation is verified in plurality of cases by plotting phase velocity and attenuation vs. frequency both for numerical solution of the full dispersion relation and for its analytical approximation, and found to be good one. Comparison to an earlier result addressing rigid rock is made; our formula turns out to closer represent the numerical solution and, besides, allows for different fluids in the layer and in the embedding medium.