  We investigate the possibility to extract information contained in seismic
waveforms propagating in fluid-filled porous media by developing and using a
full waveform inversion procedure valid for layered structures. To reach this
objective, we first solve the forward problem by implementing the Biot theory
in a reflectivity-type simulation program. We then study the sensitivity of the
seismic response of stratified media to the poroelastic parameters. Our
numerical tests indicate that the porosity and consolidation parameter are the
most sensitive parameters in forward and inverse modeling, whereas the
permeability has only a very limited influence on the seismic response. Next,
the analytical expressions of the sensitivity operators are introduced in a
generalized least-square inversion algorithm based on an iterative modeling of
the seismic waveforms. The application of this inversion procedure to synthetic
data shows that the porosity as well as the fluid and solid parameters can be
correctly reconstructed as long as the other parameters are well known.
However, the strong seismic coupling between some of the model parameters makes
it difficult to fully characterize the medium by a multi-parameter inversion
scheme. One solution to circumvent this difficulty is to combine several model
parameters according to rock physics laws to invert for composite parameters.
Another possibility is to invert the seismic data for the perturbations of the
medium properties, such as those resulting from a gas injection.
