Study On Methodology Of Azimuth Prestack Seismic Inversion For HTI Medium

In the field of unconventional reservoir exploration,fractures play an important role in hydrocarbon migration and storage.Under the different azimuth observation,because of the fractures in the reservoir,the seismic response characteristics are different,in other words,reservoirs have the characteristic of azimuthal anisotropy.Based on the azimuthal anisotropy of seismic response,a prestack seismic inversion method can be constructed to predict reservoir fractures.Due to we ignore the range of large scale offset,this method is limited to the azimuthal seismic response characteristic,it has low prediction accuracy of fracture in deep reservoir.Therefore,the development of azimuth prestack seismic inversion method for deep-layer fractured reservoirs has important research significance and practical value.Considering the influence of elastic parameter disturbance terms on the accuracy of P-wave reflection coefficient,we construct a new approximation of P-wave reflection coefficient for HTI medium based on the azimuth observation system.Due to the development for high-angle oriented cracks in deep-layer fractured reservoirs,based on the equivalent medium theory,this kind of reservoir can be abstracted into HTI medium to research the reflection and transmission characteristics of seismic wave.Based on the reflection and transmission characteristic equation for HTI medium,with the combination of perturbation theory and medium decomposition theory,the first-order perturbation approximation and the second-order perturbation approximation of the P-wave reflection coefficient for HTI medium can be constructed under the azimuth observation system.These equations break through the small angle applicability of the traditional linear approximation equation and improve the accuracy,which provide a theoretical foundation for the azimuth AVO analysis and the prediction of fracture reservoir parameters.Based on the azimuthal anisotropy of seismic data,a wide-azimuth AVO analysis method for HTI medium is constructed.Considering the difference of seismic data under azimuth observation,we construct the intercept-gradient equation for HTI medium based on the first-order approximation.Through the trail calculation of model data and actual data,the feasibility of predicting fracture density and direction based on AVO property ellipticity is analyzed,which provides the theoretical support for effective prediction of fracture.Considering the azimuthal reflection coefficient approximation,we construct an azimuth prestack seismic inversion method for high-angle fractured reservoirs.Young’s modulus is an important parameter to characterize the mechanical properties of reservoir.Based on the first-order perturbation approximation,a six-item approximation equation based on azimuthal Young’s modulus is constructed.And with the combination of Bayesian inversion theory,a prestack seismic inversion method based on azimuthal elastic impedance is constructed.Through the trail calculation of model data,this method can achieve multi-parameter simultaneous inversion,which improves the stability of seismic inversion method.Due to the azimuthal anisotropy of the Young’s modulus,a fracture prediction method based on the azimuthal Young’s modulus is constructed.Young’s modulus has azimuthal variation characteristic,the ellipticity is used to indicate the fracture density and direction.It is known that the quantitative relationship between the symmetry plane direction and the Young’s modulus of the symmetry axis direction can be directly used to invert the anisotropic parameters.The AVO property and the orientation Young’s modulus ellipticity fitting result can be used to predict the fracture density.Finally,a set of crack identification method technical route for fracture-type reservoirs is constructed,it realizes multi-method prediction of reservoir fractures which has higher universality.