Analysis Of Imaging Technique Difficulties And Error In Complex Seismic Wave Field

The post-stack depth imaging methods of complex structure include :post-stack inverse time depth migration; common non-Kirchhoff migration methods; new mixing method depth migration. Common non-Kirchhoff migration methods are mainly discussed in this paper, such as shift me thod,Phase shift plus interpolation method,Split-step Fourier method and Fourier finite difference method. Compared with Kirchhoff migration, despite the imaging method based on wave field extrapolation has relatively large calculated amount, but when dealing with complex structure has its advantages. Based on one-way wave equation,wave field extrapolation two-dimensional post-stack imaging method continues to downward extrapolating the surface wave field and then apply the imaging condition for imaging. Because of high precision imaging, so the method is widely used in two-dimensional seismic imaging. Principle of wave field extrapolation to Shift,Phase shift plus interpolation,Split-step Fourier and Fourier finite difference operator are one by one introduced. Under the complex structures and greatly speed changes geological condition, seismic records received on the surface have become very complex, so that seismic data processing and interpretation become very difficult. At this point, improving migration profile quality and enhancing efficiency becomes especially important. On the basis of programming phase shift and phase shift plus interpolation operator,view of the actual problems,phase shift and phase shift interpolation methods to improve the technical,mainly in the following areas:End effect and absorption treatment (spatial and wave number domain),Low-speed migration method,Analysis of the phase shift factor,aim to improve migration profile quality and enhance efficiency though the method of improving the accuracy.In the complex structure areas, in order to imaging precisely, pre-stack depth migration is necessary. Wave equation pre-stack depth migration is one of the most effective means for complex structure imaging,it not only can solve the steep dip imaging reflective layer, but also deal with the wave propagation and imaging problems in lateral velocity medium. The principles and processes of common-shot pre-stack migration and Plane-wave pre-stack depth migration are described in this paper. Based on one-way wave equation plane wave pre-stack depth migration method is proposed and achieved. In the process of wave field extrapolation,Fourier finite difference method(FFD)is used to adapt the situation of severe lateral varying velocity,International standard Marmousi model data used as a numerical trial examples, the validity and effectiveness of the method confirmed. The application of the method further studied to specific target imaging with different structure characteristics and seismic illumination analysis.