Effect of Pore-Filler on the Propagation of Rayleigh Waves in Quasi-Saturated Porous Medium

Abstract

The propagation of Raleigh waves at free boundaries of solid-quasi-saturated porous media and gas-quasi-saturated porous media is compared in this paper. Based on the equivalence theory, a small amount of solid particles embedded in pore-water of solid-quasi-saturated porous media, or small amount of gas embedded in pore-water of gas-quasi-saturated porous media, together with the pore-water, are equivalent to a new pore-fluid. The dispersion relation modeled by Biot theory is derived, to study the influence of the pore-filler and saturation on the phase velocity of body and Rayleigh waves. Numerical analysis is carried out on pore-space gas hydrate-bearing sediments and slight gas-bearing sediments. It is found that the types of pore-filler have great influence on the phase velocity. The presence of gas hydrate in the pore slightly increases the velocity of P1-wave and S-wave, but has little effect on the Rayleigh wave. But even a small amount of gas in the pore can significantly reduce the velocity of P1-wave. The velocity of S-wave is almost independent of saturation in gas-quasi-saturated porous media, and under the influence of P1-wave, the velocity of Rayleigh wave decreases rapidly and then tends to stabilize with the decreases of saturation. The effect of the type and saturation of the filler is influenced by the dry-frame stiffness.