Estimating frequency-dependent viscoelastic fluid indicator from pre-stack F-AVA inversion

Key words:  viscoelastic fluid indicator  frequency-dependent AVO/AVA  dispersion attributes  Bayesian estimation  fluid identification

Abstract:

The phenomenon of velocity dispersion and amplitude attenuation will occur when seismic wave propagates in oil and gas reservoir. The viscoelasticity of subsurface media is introduced to simulate the attenuation and dispersion effects of seismic waves. Considering the viscoelasticity of medium, the propagation process of seismic wave in complex medium can be better simulated. Frequency-dependent viscoelastic fluid factor is constructed to quantitatively characterize the dispersion magnitude caused by pore fluids. With the Futterman approximate constant Q model, the approximate equation of viscoelastic frequency-dependent AVA (F-AVA) reflection coefficient is derived, which keeps a good agreement with the viscoelastic Zoeppritz equation. The accuracy and feasibility of the proposed equation are systematically ascertained. Furthermore, the mapping equation and objective function of F-AVA inversion are proposed by jointing continuous wavelet multiscale decomposition, Bayesian estimation framework and priori model regularizations together. And, the iterative reweighted least squares (IRLS) algorithm is utilized to solve the objective function. Model tests and a field case illustrate the anti-noise and practicability of the inversion method. Compared with the conventional dispersion attributes, the inversion result of the frequency-dependent viscoelastic fluid factor has less 'false bright spot interference, which proves the effectively in reservoir pore fluid identification.