Capillary forces in thea coustics of patchy-saturated porous media

A linearized theory of the acoustics of porous elastic formations, such as rocks, saturated with two different viscous fluids is generalized to take into account a pressure discontinuity across the fluid boundaries. The latter can arise due to the surface tension of the membrane separating the. fluids. We show that the frequency-dependent bulk modulus (K) over tilde(omega) for wavelengths longer than the characteristic structural dimensions of the fluid patches has a similar analytic behavior to the case of a vanishing membrane stiffness and depends on the same parameters of the fluid-distribution topology. The effect of the capillary stiffness can be accounted for by renormalizing the coefficients of the leading terms in the low-frequency limit of (K) over tilde(omega). (C) 2003 Acoustical Society of America.