Study On QP Wave Modeling And Reverse Time Migration Methods In TI Media

With the deepening of seismic exploration and the complexity of reservoir,anisotropy are gradually taken into account. Migration methods based on the isotropictheory can not effectively solve the anisotropy imaging problem, and the accuracy ofimaging also can not be guaranteed. So It is necessary to develop a migration methodbased on anisotropic theory. Reverse time migration (RTM) have superiority to theother methods, such as high imaging accuracy, no inclination limit, and meeting thecomplex medium imaging requirements. Currently, mostly underground anisotropicmedias are TI medium (transversely isotropic medium). Therefore, the migrationmethod based on anisotropic theory has been taken more attention in geophysicalseismic exploration. However, in the anisotropic medium, P-wave and S-wave arecoupled in its elasic wave equation, so it is hard to directly implement anisotropicelasic wave RTM into reality for the difficult to obtain elastic parameters and its largecalulation expense.Thus, based on the results of previous resarch, this paper foucs on the quasi-Pwave euqation reverse time migration in TI anisotropy medium by approximatemethods, without considering share wave. The main research work and progress asfollows:(1) In weak anisotropy approximation and acoustic approximation for commonmethod, this paper calculated and analysised the differences in accuracy of the phasevelocity equation and the dispersion relation equation, considered this twoapproximate dispersion relations within the certain error range is exact in TTI medium,and the Alkhalifah acoustic approximation has higher accuracy than the weakanisotropy approximation.(2) This paper derived a first-order numerical method for Alkhalifah acousticapproximation equation methods. Numerical simulation have been done for testing.And that fully explain the effects of anisotropy can not be ignored by the theoretical model analysis of the trial results. For obvious effect of anisotropic subsurfaceseismic data areas, isotropic reverse time migration has been unable to meet the need,we must study anisotropic reverse time migration imaging method for better imagingresults.(3) Through the acoustic fourth-order partial differential equations approximatereduction, we derived second-order coupled qP wave equation in the form of simple,and it iseasy to implement and can be easily extended to TTI media. In this paper, thedifferent forms of second-order wave equation coupled qP done when numericalsimulation and experimental analysis and comparison of reverse migration that theresults are consistent. While taking advantage of the wave field rotation and parametersubstitution, the paper deduced qP wave equation of the second order coupling underTTI media and analyze its stability problems.(4) In the study of traditional VTI media coupled qP wave equation reverse timemigration, based on the use of VTI media precise dispersion, we derived the VTImedia pure P-wave coupled with pure SV-wave approximation using a Taylorexpansion order, its derivation do not need set the shear wave velocity to zero, so ithave more accurately describe the kinematic characteristics of quasi-P waves, solvedthe stability and solverd pseudo SV-wave interference problem, and extended to morecomplex symmetry axis tilt TTI medium to go. Meanwhile, based on these studies andthrough the application of pseudo-analytical method, the paper realized the pseudo-analytical method of offset VTI/TTI media pure P wave equation based numericalsimulation and inverse to solve numerical problems.