Effects of pressure and saturating fluid on wave velocity and attenuation in anisotropic rocks

We obtain the energy velocities and quality factors of anisotropic reservoir rocks as a function of pore pressure. partial saturation and frequency. The model is based on Biot's poroelastic theory for anisotropic media. The directional dependence of attenuation is obtained by generalizing the eigenstiffnesses of the undrained medium to relaxation functions (six at most, depending on the material symmetry). The frequency dependence of attenuation is described with constant-Q kernels associated with each eigenstiffness, and viscodynamic functions to model the high-frequency behavior. We apply a uniform gas/fluid mixing law that satisfies Reuss's and Voigt's averages at low and high frequencies, respectively. thus. simulating the unrelaxed state due to nonuniform-patchy-saturation (segregated fluids). Pressure effects are accounted for by an effective stress law. (C) 2003 Elsevier Science Ltd. All rights reserved.