Numerical Simulation And Analysis Of Seismic Dispersion And Attenuation In Fluid-saturated Porous Media

The frequency-dependent attenuation and velocity dispersion of seismic response are closely related to hydrocarbon reservoir.The fluid in the porous medium has a great influence on the propagation of seismic waves,and the corresponding characteristics of the seismic response will also change,which are the useful information needed by the seismic exploration.In order to further explore the effect of pore fluid on the seismic response characteristics of the reservoir,we derive a new wave field extension method based on the Diffusive Viscous Wave equation(DVWE)and apply a stable extended local Rytov Fourier approximation within each extrapolation depth interval.The new method considers the presence of pore fluid in the porous rock,which causes attenuation and dispersion by the mechanism broadly known as wave-induced fluid flow(WIFF).In addition,the method can accommodate to the lateral variations in slowness,diffusion coefficient and viscosity.The deep seismic data shows that the energy is weak and the SNR is low,especially when the wave impedance difference between the reservoir and the surrounding rock is smal,and the amplitude of the reflected wave in the seismologica l record will also weaken.The recognition technology for deep dim spot reservoir with low porosity and low permeability has not been greatly developed.In this paper,the dynamic equivalent medium theory of Chapman and the frequency dependence AVO analysis method are combined to simulate the AVO reflection characteristics of low porosity and low permeability reservoir.That is,the inversion phenomenon of the reflection amplitude appears with the increase of the incidence angle.This phenomenon reveals the possible occurrence state of the dim spot reservoir and provides a certain theoretical basis for the actual seismic exploration and development.In this paper,based on the equivalent medium theory of multiphase fluid,the phase velocity and the inverse quality factor are obtained.This theory is bases on White's patch saturation model that improved by Johnson,which considering the relations hip between the dispersion length corresponding to the high frequency,the intermed iate frequency and the low frequency.Then,we analyze the pore fluid flow induced by different frequency seismic waves.Furthermore,it is found that the frequency dependent attenuation and velocity dispersion caused by the fluid flow induced by seismic waves is larger.On the basis of summarizing and analyzing the influence laws of different physical parameters on seismic wave propagation characteristics,the analysis of wave field propagation characteristics is further combined with forward numerical simulation to provide guidance for the prediction of actual fluid reservoir.In this paper,the phase velocity corresponding to different permeability,gas saturation and patch radius are calculated by using the above theory.The phase velocity variation of fluid porous media is applied to a complicated braided channel reservoir model,and the derived wave field simulation method is applied to the braided channel model.The numerical simulation results of DVWE method and conventional acoustic wave equation(AWE)method are given,respectively,and the dispersion and attenuation caused by gas sandstone reservoir are compared and analyzed.The further study shows that the gas saturation of the reservoir has an influence on the seismic characteristics of the seismological records.It has a potential significance for the reservoir indicator.