The Research On Traveltime Tomography Method Based On ADCIGs In VTI Media

Earth's media were generally considered to be isotropic in early studies in the field of geophysics.However,in recent years,more and more theoretical research and field exploration has confirmed that the Earth's media have anisotropic features universally.If anisotropy is not taken into consideration,there will be difference between stacking and vertical velocity,which will lead to deviation in offset depth,and seriously affect the imaging accuracy and effect of media inside and the area under tilted reflector.In addition,with the improvement of field seismic acquisition ability and technological progress,the long offset and three-dimensional wide azimuth angle seismic data collection has come true.Therefore anisotropy has made increasingly negligible impact on seismic exploration research.As the study of imaging and velocity modeling based on isotropic media hypothesis is difficult to meet the requirements of accurate imaging on complex structures,it is very necessary to carry out the research of anisotropy.In this paper,we first state the significance of the research on anisotropic inversion.Then,based on the classical anisotropy theory,we introduce the characteristics of anisotropic media,and discuss the parametric patterns,phase velocity and group velocity in VTI media emphatically.Then we build the VTI medium tomographic equations by applying Taylor series on forward process.And based on the phase velocity of P wave whose shear wave velocity is set to be zero,we get the specific expression form of VTI tomographic inversion equation.We adapt Gaussian beam ray tracing method to get ray path,anisotropic Gaussian beam imaging method to obtain the angle gather and the LSQR algorithm to solve the inversion equation.Then,based on the study on the sensitivity degree of anisotropy parameter,we improve the conventional sequence strategy in single parameter inversion and propose the angle constraint inversion strategy.To improve the accuracy and instability of the parameter inversion in the joint inversion we introduce the normalized matrix and adapt the three-step inversion method.In the end,through several theoretical models we further optimize the inversion process and prove that the method is accurate and stable.