Synthetic Source Record Interactive Residual Migration Velocity Analysis Based On Controlled Illumination

The project related to synthetic source record residual migration velocity analysis is studied in this dissertation. It includes split-step Fourier prestack depth migration (PSDM) by velocity partition to get better imaging quality, sparse frequencies PSDM method to improve the computational efficiency, and synthetic source record interactive residual migration velocity analysis based on controlled illumination on the basis of the two methods mentioned above.Perturbation method is the theoretical basis of split-step Fourier (SSF) method, and the errors of its will become large when there is strong lateral velocity variations. According to the error analysis of perturbation method, a wavefield continuation method by velocity partition is presented in this dissertation. When lateral velocity has rapid variation, the velocity partition is implemented according to velocity distributing and different reference velocities are used in each velocity zone, which can greatly increase the imaging quality and at the same time greatly reduce the number of reference velocities. This method can be used especially for imaging complex structures and has been applied to the SSF method and the local Born approximation method. Both the 2D Marmousi data set and the SEG/EAEG 3D salt model examples showed that the imaging quality of this method is much better than that of SSF method and is comparative to and even partly better than that of FFD method.The synthetic source record PSDM method reduces the quantity of seismic data needed to migrate and thus improves the computational efficiency. Furthermore, the sparse frequencies synthetic source record PSDM method is proposed which can reduce the computation cost by sparsely resampling of frequencies. By selecting a fit coefficient, the computation cost using this method is only one-third or quarter of the original method with maintaining imaging quality.The synthetic source record PSDM based on wave theory is adopted in synthetic source record interactive residual migration velocity analysis method based on controlled illumination, and is combined with velocity partition method and sparse frequencies method which can improve the imaging quality and computational efficiency. By using the controlled illumination technique, the severely distortion of the plane wave caused by the lateral velocity variation is avoided which keeps the consistent ray parameters in both migration and velocity analysis, and the difficulty that the velocity correction formulae can not be used directly under the irregular surface is overcome. The practical velocity spectrum makes the interactive residual migration velocity analysis feasible and convenient. The results of 2D salt model, field data of Xinjiang and 3D model prove that this method is valid and practical for migration velocity analysis.