Key Technology Of Method Of Phase Shift For Wave Field Simulation And Imaging Research And Application

Phase shift method was created by J.Gazdag on1987for the first time and realizing it by synthesizing seismogram (zero-offset) and could get an accurate vertical velocity shift effect comparing to Stolt’s F-K law and Kirchhoff method and have excellent advantage of weak dispersion, good stability, non-limitation of steep stratum angle, this is an ideal wave field imaging method comparing with J.Clearbout’s finite difference method. But when the seismic event continue downwardly, this could cause boundary effect (end effect) in this process of wave field downward and appear strong interference seismic event in migration cross-section, in most cases, the will degrade cross-section signal-to-noise ratio. To solve this problem, A.A.Dubrulle and J.Gazdag created method of adding zeros at sides of record boundary in1979, although zeros method can be used to eliminate the boundary effect, but it increased the amount of data more than two times artificially and decreasing calculative efficiency, increasing the amount of computer memory.1983-1984He Zhenhua, J.Nai, and GH.F.Gardner used the method of space domain boundary absorption to solve the boundary effect well. However, because of absorbing boundary conditions realizes in the spatial domain, while the wave field continuation realizes in the wavenumber domain, we have to do a Fourier transform and a Fourier inverse transform in each extension step along the direction of the extension step space. The calculation speed is slow when there are the many number of continuation steps. To solve this problem, J.Gazdag proposed method of phase shift plus interpolation to realize the problem of horizontal velocity shift in stratum.This thesis studies the basic theory of phase shift of wave equation, writing the phase shift method for wave field forward program and the phase shift method and the phase shift interpolation method migration programs, using dotting impulse and modeling discussed the influence of phase shift factor, speed of modeling and migration imaging, then proposed the best speed fitting for the phase shift method.Because of boundary effects is the main factors that affect the phase shift method, the previous method made by predecessor is very effective, but the computational efficiency is very low and would occupy a large number of computer memory. According Learning and research results of previous studies. I propose the method of absorption in wave number domain, and verify the effect of the wave number domain absorption method by the dotting impulse and model. Wave number domain absorption do not do the Fourier transform and inverse Fourier transform in the special domain, thus the computational efficiency is very high. But there are still some other problems about Wave number domain absorption, such as the problem of curvature after imposing absorption coefficient, the speed problems etc. This thesis also analyzed and discussed, and finally using the actual shallow and deep seismic data to verify the correctness of migration in wave number domain absorption.