Preserved-amplitude Common Focus Point(CFP) Migration In Areas With Complexity

Along with the increasing difficulty of the seismic exploration and oil/gas development,also with the increasing complexity of the reservoir, the requirement of the seismic exploration precision is more and more high, now the migration method not only can offer the phase information of the surface structure, but also can provide the amplitude which is in ratio to the reflection coefficient, then Preserved-amplitude prestack migration is more and more popular.The common focus point technology is a new seismic migration method, it based on the principle of the equal travel time, can realize the migration by two focusing steps (that is focusing in emission and focusing in detection), its technical advantage is that not needing the correct velocity model, by the iteration of the focusing operator, it can get the correct velocity model and final correct migration result. In the past, researchers realize the CFP migration based on the ray theory, the method's capacity is high, but the migration precision does not satisfy the requirement of the preserved amplitude migration. This thesis based on the wave equation theory come true the two focusing steps, by the wave equation theory get the CFP gather, We fully considere the influences of wave front diffusion, design the amplitude-preserved operator which can eliminate the effect of receivers and propagation, based on the wave equation extrapolation preserved amplitude operator improve the preserved amplitude of the algorithm,finally get the true amplitude migration result of the CFP method by the preserved amplitude migration condition. Comparing the preserved amplitude CFP migration based on the wave theory with the common CFP migration, the precision of the result is higher, it can compensate the loss of the geometric diffusion.We achieve the redatuming based on the common focus point method by the two focusing steps, the key of the method is the generation of the focusing operator, by the redatuming wo can elimate the influence of the rugged topography to the sub-surface structure, its processing result is better than the conventional time shift static, and the shortcoming of the method is the new record after CFP-based redatuming by the influence of the focusing steps has lower S/N ratio, the energy of the middle and deep zone after the redatuming is lower, this is the aspect that we improve in the future.Using the common focus-point technology to the migration of the irregular surface, by the synthesis focusing operator and the theory of synthesis areal source,"wave field downward continuation"based on accumulating step by step is a valid way to solve the problem of irregular surface common focus point migration. The method first synthesizes the synthesis focusing operator of the irregular surface, then uses the theory of synthesis areal source to generate the common focus point gather, and at last gets the migration result based on the irregular surface according to the wave equation continuation. The key of the method is how to combile the CFP technology and the wave equation continuation theory. the calculation efficiency is improved, we can only choose a few of the focusing points, then get the migration result which is similar to the conventional common shot-records gather migration result. Further using the preserved amplitude wave equation continuation operator and the smooth function migration condition,then we can get the preserved amplitude migration result based on the CFP gather. Tests on model and actual data processing show the validity and the practicability on the complex surface migration. Comparing with the common CFP migration, the precision of the result is higher, it has good migriaon quality of the target layer,and can compensate the loss of the geometric diffusion.