Sparse Frequency In The Research And Application Of Pre-stack Migration

Migration is one of the most important methods in seismic data processing,its purpose is to obtain a more realistic information of underground structures through the correction of unprocessed data.With the improvement of computer computing ability,pre-stack depth migration gradually replace post-stack migration and time migration,which became the main migration method in practical application.Pre-stack depth migration based on the wave equation can deal with lateral variation of medium velocity,can be more accurate imaging of complicated geological structure.However,Depth migration based on wave equation is not only a large amount of calculation but also the computation efficiency is low,how to improving depth migration computation efficiency under the premise of keeping imaging precision is a problem urgently need to solved.In order to improve the calculation efficiency of pre-stack depth migration,to reduce computational cost and imaging noise,we choose to implement depth migration in frequency domain,first of all,it can avoid the dispersion of difference,being better imaging accuracy than depth migration of time domain in theory,Second,it can also have more methods to improve the computational efficiency.In this paper,the Fourier finite difference(FFD)as the foundation migration method,the main research the effective method to improve pre-stack migration operation efficiency in frequency domain.First,the synthetic source record method can synthesize single source records into a synthetic source record,so that one can reduce the amount of migration data effectively.Synthetic source and synthetic source record technology multiple reduce the amount of calculation and provide a lot of convenience of compute and processing data in pre-stack migration,which not only can keep the precision but also has a high computational efficiency.Second,the wave equation is solved in frequency domain,each frequency panel of the data carries information on the reflectivity after a Fourier transform of the time-domain seismic data,some of them are redundant,be appropriate to reduce the number of frequencies in wave field extrapolation with the purpose of improving the pre-stack migration computation efficiency,this gain is mainly accomplished by using a more effective subset of the available frequencies.However,the choice of frequencies cannot be arbitrary,if the frequency sampling spacing is too large,the wrap-around artefacts can occur in the image.We conclude the frequency sampling condition that can avoid wrap-around artefacts by analysis and proof,with two models have been used to test the correctness and validity of the selected frequency method.