The Research Of Gaussian Beam Migration Methods In Time Domain For Vertical Transversely Isotropic (VTI) Media

Seismic exploration is the most effective method to find the oil and the gas in geophysical exploration.As an important method of data processing in seismic exploration,seismic migration technique can transform seismic data into underground geological structure profile.The traditional migration method assumes that the underground medium is isotropic.But the research shows that the anisotropic medium exists widely in the underground medium.If anisotropy is neglected in the process of migration imaging,the imaging position will be inaccurate and the structure will be distorted.Therefore,the anisotropic medium migration method can improve the imaging accuracy.Imaging efficiency is also very important in practical production.Gaussian beam migration is an accurate and efficient depth migration method.This method is an improvement of the Kirchhoff migration method.It retains the high efficiency of the Kirchhoff method,and can also accurately image the caustic region and shadow region.However,the previous Gaussian beam migration was mainly carried out in the frequency domain,and the method must calculate the green's function and the backward wave field of all frequencies at the imaging point.However,in the time domain,we can only calculate the green's function and the backward wave field at the time of the wave arrives at the imaging point.The Gaussian beam migration in time domain is more efficient than that in frequency domain.Based on the above problems,this paper studies the Gaussian beam migration method in time domain of anisotropic media.Based on previous studies,the Gaussian beam migration method in frequency domain for VTI media was developed into the time domain,and the Gaussian beam migration method in time domain for Vertical Transversely Isotropic was proposed.The research content includes the following three aspects:(1)We derived the basic formula of Gaussian beam through ray tracing system and introduced the basic property of Gaussian beam.(2)We derived the kinematics and dynamics ray tracing formulas for anisotropic media that studied by Zhu and simplified the coefficients of the equations.Gaussian beam imaging formula in time domain studied by Gao was derived in this paper.The simplified ray tracing algorithm is applied to Gaussian beam migration in time domain.The results of model trial calculation and the application of practical data show the correctness of the method.(3)We studied the converted wave ray tracing systems for VTI media and simplified the coefficients of the equations.Based on the research of Li zhenchun,the formula of converted wave Gaussian beam imaging in time domain is derived,and the converted wave Gaussian beam migration imaging method in time domain for VII media is proposed.The experimental results show that the proposed method is correct and effective.