The theories developed by White and co-workers describe the complex
moduli of a medium partially saturated with spherical gas pockets
and those of stratified layers composed of two heterogeneous porous
media. A generalization to gas patches of arbitrary shape has been
given by Johnson. These models represent the mesoscopic-loss mechanism,
which is one of the most significant causes of attenuation of seismic
waves in reservoir rocks. Comparison of White's and Johnson's models
show that, as the patch shape complexity increases, the patch geometry
affects much more the relaxation frequency than it affects the maximum
loss. The simulation of synthetic seismograms requires solving Biot's
differential equations with very small grid spacings, because the
loss mechanism involves the conversion of fast P-wave energy to diffusion
energy in the form of the Blot slow wave. Because the wavelength
of this wave can be very small, the poroelastic solution requires
a very large amount of storage and computer time. An efficient approach
is to approximate White's moduli by the Zener model and then solve
the single-phase viscoelastic differential equations. (C) 2009 Elsevier
Ltd. All rights reserved.