Full Waveform Inversion Of QP Waves In Transversely Isotropic Medium

Anisotropy is generally present in the earth.At present,the relatively seismic exploration technology is mostly based on the assumption of anisotropy,and there is a lack of theoretical research on anisotropy.In the subsurface where fractures and thin interbeds are developed,the strata mainly show transverse isotropy(TI).Therefore,the study of full waveform inversion in TI medium is of great significance to search for underground fracture-vape reservoirs.As a high-precision imaging method in seismic exploration,full waveform inversion has attracted more and more researchers’ attention in recent years.Therefore,based on the pseudo-acoustic wave equation in TI medium,this paper carries out corresponding forward modeling and inverse time migration,and extends the study of full waveform inversion to TI medium.The inversion of velocity parameters in TI medium is completed by using conjugate gradient method.For the propagation of seismic waves in TI medium,researchers have also done a lot of research work,among which the main research object is the numerical simulation and inverse time migration of quasi-P wave.Therefore,based on the previous research results and theories,this paper simplifies the corresponding forward equation through the weak anisotropy approximation method,aiming at the numerical simulation research of q P wave in TI medium.It is further extended to full waveform inversion.The main research work and progress are as follows:(1)The acoustic approximation method is used to derive the q P wave equation in TI medium,and the staggered grid high order finite difference is used for numerical simulation.It is found that the forward operator adopted in this paper can simulate the quasi-P seismic response characteristics in TI medium more accurately.(2)In view of the quasi-longitudinal wave equation adopted,the corresponding governing equation with PML boundary conditions is derived and the model trial calculation is carried out.The source ring method is used to suppress the S-wave artifacts in forward modeling in anisotropic media.(3)The calculation formula of the gradient in the full waveform inversion of the pseudo-acoustic wave equation based on the conjugate gradient method is derived.Due to the need of subsequent research,the trial calculation of the inverse time migration in TI medium is carried out first.It is found that the pseudo acoustic wave equation used in this paper can restore the underground geological structure.(4)The q P wave equation in TI medium is extended to full waveform inversion,which basically realizes the purpose of restoring underground geological structure.How to obtain higher precision imaging effect and improve the inversion rate still needs to be further studied.