3D Parallel Prestack Depth Migration Of Synthetic Source Records

The project related to 3D prestack depth migration of synthetic source records is studied in this dissertation. It includes common-offset prestack time migration, 3D parallel prestack depth migration of synthetic source records, adaptive spatial-division split-step Fourier migration method and residual migration velocity analysis by synthetic source records.In common-offset prestack time migration the formula of poststack phase shift migration is generalized to common-offset section for constant-velocity medium. The formula of phase shift migration of common offset sections is obtained by numerical fitting method. This migration method takes vertically varying velocity into account by defining average velocity. Theoretically, only when velocity is constant, is the formula accurate. However, synthetic and real examples indicate that data with reasonable rapid vertical velocity variation can also be imaged effectively.The shot sources and sources records can be synthesized by three properties of wave equation operator without any physical assumption, moreover, in terms of three synthetic formulae we unify area shot records synthetic method and phase encoding synthetic method under one theoretical framework. The method is flexible and selectable by designing different synthetic operator for different input data sets. Prestack depth migration method of synthetic source records retains accuracy of shot profile migration and overcomes high computational cost. The realization of parallel programming with MPI speeds up the computations. The test of 3D SEG/EAEG salt C3-NA data set and Sinkiang land rugged topograph seismic data set show that the method is efficient and practical.The reference slowness of adaptive spatial-division split-step Fourier migration method is determined by an error parameter of the perturbation term in split-step Fourier operator and whole velocity field variation. One reference slowness and its corresponding local slowness make up a division, which comprises several spatial discontinuous subdivisions commonly. The number of reference slowness is effectively reduced. The choice of reference slowness, including the number of reference slowness and construction of spatial divisions, is adaptive and more reasonable at each depth step. A simple and economical smoothing filter in the wave number-frequency domain is designed to avoid artifacts of the extrapolation of wave field in the presence of sharp discontinuities in the velocity field. The performance of the method is demonstrated on 2D models.Estimating the macro velocity model is considered to be the key step of prestack depth imaging procedures. We proposed residual migration velocity analysis by synthetic source records based on residual migration velocity analysis in the plane wave domain. The analytical equation is used to perform residual migration after prestack depth migration of synthetic source records. An interactive velocity analysis procedure is designed to build avelocity-depth model. Controlled illumination source is used for reducing the error resulting from aberration of plane wave transmitting complex geology structure. The correctness and effectiveness of the method is proved by the numerical experiments on the theoretical model and field datasets.