Wave Equation Pre-Stack Depth Migration And Migration Velocity Analysis In Complex Media

With the development of oil and gas exploration, exploration targets and conditions have become more and more complex, in order to effectively solve the exploration of complex surface area or complex oil and gas reservoir, it is necessary to develop the new migration imaging algorithms, applicable to the complex medium, and obtain precise migration velocity. Based on the above described, the thesis studies some key issues in the wave equation prestack depth migration and migration velocity analysis, and has better applied value and practical significance for wave equation migration and migration velocity analysis in complex areas. The studies in this thesis mainly focus on the following aspects:(1) The thesis studies common migration operator and amplitude-preserved migration operator, and verifies advantages of the amplitude-preserved migration operator. Through post-stack forward and migration based on theoretical models, the thesis makes a summary about adaptability of various migration operators, and provids the references for practical application.(2) The thesis evaluates migration algorithms using one-way wave pre-stack forward wave-field simulation, avoiding the weakness of two way wave, and analysises the waveform distortion caused by complex surface through comparing wave field characteristics of horizontal surface and relief surface, and provides the basis for understand correctly wave-field characteristics in complex geologic condition.(3) The thesis realizes the pre-stack depth migration algorithms based on single square root and double square root, although the two algorithms are equivalent theoretically, but have larger differences in pratical applications. The thesis compares the similarities and differences between two algorithms, and verified that double square root migration is more efficient, and is more better to output the offset domain common image gathers or angle domain common image gathers for migration velocity estimation and AVO/AVA analysis.(4) The amplitude-preserved migration operator based on double square root is applied to common image gathers extraction for the first time, and ensure the correctness of amplitude energy features. The adaptability of common image gathers for multi-ray paths has been studied. On this basis, the thesis analysises the sensitivity of various common image gathers for migration velocity through the residual curvature analysis and depth-focusing analysis, and proves the feasibility of applying common image gathers to migration velocity analysis, and provides the study foundation for migration velocity modeling.(5) The thesis realizes migration and common image gathers analysis by replacing the serial algorithms with parallel algorithms based on MPI parallel technology, and achieves high parallel efficiency and speedup. In order to adapt to the development and application of multi-core technology, multi-level parallel method of migration and velocity analysis based on MPI and OpenMP is proposed, the method gives full play to multi-core performance considering load balancing, and has broad application prospects.(6) The thesis processes practical data about some exploratory area on sea in our country. After the interactive migration velocity analysis for practical data, the higher accuracy level velocity model has been obtained, and it is applied to pre-stack depth migration, the migration imaging result is better. Common image gathers obtainted by migration verifies the correctness of level velocity model.