ALBERT

Description: 〈span〉〈div〉SUMMARY〈/div〉Understanding the fluid dependence of poroelastic constants of a layered porous package is important for various aspects of applied and fundamental geosciences. To decouple the effects of fluid substitutions and anisotropy in a layered package on vertical stiffness constants, a set of approximations to anisotropic fluid substitution theory is introduced in conjunction with Thomsen's anisotropy parameters. Validation of the approximations is performed by physical modelling and theoretical examples. In physical modelling, synthetic porous layers are used and interbedded by Plexiglas sheets to build a layered transversely isotropic symmetry with a vertical symmetry axis package. Seismic acquisitions over the physical model saturated with air, oil and water are carefully conducted, respectively. The reflection amplitudes are properly corrected and inverted by a specific seismic inversion scheme to recover 〈span〉P〈/span〉- and 〈span〉S〈/span〉-wave impedances. Poroelastic constants of the thin package then are deduced from the inverted results. Applying the approximations to the physical modelling results, a good match between the estimated vertical stiffness constant values of the physical model and the theoretical predictions is observed. Results of both physical modelling and theoretical analysis demonstrate that fluid substitutions when going from drained to undrained behaviour will enhance or reduce the degree of anisotropy of the medium, depending on the sign and magnitude of Thomsen's anisotropy parameter δ. Results show that the shear modulus of the individual layer plays a key role in controlling the degree of the initial anisotropy of the thin package, which directly dominates the effect of pore fluids on poroelastic constants of the upscaled medium.〈/span〉