Research On Convert Wave Velocity Analysis Method

Nowadays,seismic exploration technology is developing rapidly,and the exploration targets become more complicated.Seismic data processing and interpretation are gradually becoming an integration.Conventional P-wave exploration based on the theory of sound wave hypothesis can not provide enough information some times.So multi-component seismic exploration is gradually becoming concerned.Compared with Conventional P-wave exploration,convert wave always carry more abundant information of underground rock physical properties,which can play an important role in lithology inversion,fracture parameter extraction and gas content detection.When there is a high velocity layer or an air bearing stratum,the amplitude of P-wave can be reduced greatly,which can lead to the shielding phenomenon of the lower structure.Convert wave exploration can solve This problem.Due to higher cost of shear wave excitation,we often use convert wave instead of shear wave.Convert wave data processing is the basis for the subsequent inversion interpretation problems,however,due to the complexity of shear wave propagation mechanism,current mature conventional seismic processing method is no longer applicable to convert wave.Velocity analysis is the key to accurate imaging of convert wave,so it is important to study velocity analysis method of convert wave.This paper on the basis of previous research,put forward a series of convert wave time domain and depth domain velocity analysis method,contains stacking velocity analysis.pre-stack depth migration velocity analysis and tomography velocity inversion.Among them,stacking velocity analysis provides a reference velocity for pre-stack time migration velocity analysis,pre-stack time migration velocity analysis provides initial velocity field for tomographic inversion.Finally through tomographic velocity iterative inversion we can obtained a more precise velocity field for migration.In stacking velocity analysis part,we discussed convert wave propagation mechanism,common conversion point(CCP)calculation,gathers extraction and velocity analysis method based on common conversion point,put forward a calculation method of conversion point coordinates based on angle scanning.In the part of pre stack time migration velocity analysis,we study on pre-stack time migration method based on equivalent offset.The method need just transform pre stack data to common converted point scattering(CCSP)gathers and does ignored the complexity of conversion point calculation and the lack of offset in common conversion point gathers.It can provide higher fold number,and higher computational efficiency.After transforming to depth domain interval velocity by Dix formula,the RMS velocity field obtained by Pre-stack time migration velocity analysis method can provide higher accuracy of the initial velocity field for tomographic inversion.It can reduce the number of iterations,improve the efficiency of the inversion.Through numerical tests and field data tests and analysis,proved high accuracy and efficiency of this method.