Effect of fluid on wave propagation in weakly anisotropic porous media
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Predicting seismic velocities in isotropic fluid-saturated rocks is commonly done using the isotropic Biot-Gassmann theory. For anisotropic media, the Biot-Gassmann solution is expressed in terms of stiffness or compliance, which does not provide an intuitive understanding on the impact of fluid on anisotropy. To analyse how the pore fluid affects wave propagation in weakly anisotropic media, we rederived these expressions in terms of dimensionless anisotropy parameters. Besides, we study the effect of fluid on two anisotropy patterns, the one caused by aligned fractures embedded in an isotropic porous background and the stress-induced anisotropy pattern. By deriving an approximation of the anellipticity parameter η, we show that if the dry medium is elliptical, the saturated medium is also elliptical but only if the porosity is not too small. This result can provide a way of differentiating between stress- and fracture-induced anisotropy.
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Collet, O.; Gurevich, Boris (2016)A major cause of attenuation in fluid-saturated media is the local fluid flow (or squirt flow) induced by a passing wave between pores of different shapes and sizes. Several squirt flow models have been derived for isotropic ...
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Collet, O.; Gurevich, Boris (2013)Predicting seismic velocities in fluid-saturated rocks is commonly done using Gassmann equations. For anisotropic media, these equations are expressed in terms of stiffness or compliance tensors. To gain a more intuitive ...