The Elastic Wave AVO Forward Modeling Based On Reflectivity Method

The conventional AVO theory is based on the single phase isotropic medium theory, butthe real underground reservoir medium is fluid-filled, and the fluid saturated in the porous isviscous. When the seismic wave travel through the reservoir, the relative motion between therock skeleton and fluid will occur caused by the seismic wave effect, at the same time theviscosity attenuation will happen. These elements will play an important role of changing thequality factor Q. Therefore we must take the fluid saturated in the pore and the attenuationcaused by the fluid into consideration fully, then we can exactly describe the reflection andtransmission characteristics of the real underground media. Analyzing the seismic wavecharacteristics and AVO forward modeling of viscoelastic medium and fluid saturated porousmedium has an important sense of complicated oil and gas reservoir exploration, whatever intheoretical research or practice.This thesis illustrated the basic principle of reflectivity method forward modeling andsummarized the influence of reflectivity method. Then we put up the method to reduce thefalse frequency produced by shortage sampling and the confusion wave produced by largeangle incident. In this study, we developed a method of iterative correlation weightedcoefficient to suppress the mixed and disorderly reflection caused by sphere wave synthesisintegral truncation effect. For the sack of enhancing the compute speed, we proposed themethod and principle of stratigraphic subdivision.This paper utilized Gassmann equations to calculate some parameters when the rocks aresaturated on the basis of the given physical property parameters (porosity, the fluid propertyand so on). Then use the self-consistent theory to convert the parameters of fluid saturatedporous medium. We deduced the P/S-wave reflection-transmission coefficients at thecondition of P-wave incidence and porous isotropic media. We synthetic the seismic trace ofplane and sphere wave, then analyze the influence ingredients of AVO responses withdifferent porosity and different fluid classification.Based on the viscoelastic medium basic theory, we derivate viscoelastic mediumreflectivity method forward modeling method. We analysis the attenuation of variousmulti-layer model and different viscoelastic parameters and modeling the AVO response of viscous media. Then introduce viscoelastic medium model into the porous media elastic waveforward modeling, calculate the pore viscoelastic medium reflection coefficient of speed Pwave slow wave and S wave. Finally we analyze the pore viscoelastic medium AVOcharacteristics and the influence of AVO response caused by porosity fluid type qualityfactor etc.The study of this thesis suggested that the reflection coefficients derived from reflectivitymethod are more exact, and iterative correlation weighted coefficient method do well intruncation effect suppression. We needn’t to take the problem of decoupling the wave fieldwhile modeling with reflectivity method. In the gas reservoir model, the porosity and watersaturation both have effect on AVO response of the upper interface. Compare to watersaturation, porosity has greater impact on AVO trend. The attenuation of amplitude ofviscoelastic media is only relate to the viscosity but the impedance difference of the two sideof the interface, and both the parameters of porous and viscoelastic media have effect on theAVO modeling record. The model and real data application show that the method proposed bythis thesis do realize the AVO forward modeling of fluid saturated porous and viscoelasticmedia.