Study On Kirchhoff Pre-stack Depth Migration Method For Transversely Isotropic Media

Conventional seismic processing assumes that the earth media is isotropic.But anisotropy is a common characteristic in the crust rock.Besides,when the seismic wave is spreading in inhomogeneous isotropic media which single layer thickness is much shorter than the seismic wave length,the propagation can be treat as in homogeneous transversely isotropic media.The difference between the assumption and reality causes the migration error and migration noise.To the anisotropy caused by rock particle with directionality,the parallel fractures,and fine periodic thin layers,transversely isotropy is a proper approximation.According to statistics,most sedimentary rocks have the characteristics of transversely isotropy.Hence,studying on the propagation principle and migration method of isotropic media has great meaning for reducing the migration error and improve the resolution and S/N ratio of the seismic map.Corresponding research was made on the anisotropic seismic wave propagation theory and Kirchhoff integral migration method.Firstly,the research begins with the constitutive equation,differential equation of equilibrium and geometry equation to derive the wave equation of seismic wave in isotropic media.Method of staggered grid finite differential modelling and method of phase velocity and group velocity calculation was studied.And the polarization direction between the isotropic and anisotropic media was compared to introduce the method of wave mode separation.Based on the research,this paper introduced the designation and implement of the transversely isotropic media seismic modelling software and phase velocity and group velocity calculation software.Then,Kirchhoff diffraction theory and Kirchhoff integral modelling method was introduced.And this paper introduced a water-layer multiple prediction method which is based on Kirchhoff diffraction theory.This method predicted the water-layer multiple very precisely.Combining with the curvelet domain multiple subtraction technology,water-layer multiple was subtracted.The resolution and S/N ratio were improved.And then the ray tracing system and Kirchhoff pre-stack depth migration was presented.The image condition,migration aperture,weight function and alias frequency suppress method was discussed.Synthetic data and field data tests proved that the method in this thesis can image the transversely isotropic records precisely.The diffraction was convergent and the structure was clear.