Application Of Offset Domain Grid Tomography On Dabei Structure

Three sets of high-speed conglomerate layers are developed in the Dabei Research Area.The geological structure is complex,the formation is steep,the velocity changes sharply and the velocity spatial distribution is complex.Accurate modeling of the velocity is difficult.However,velocity is an important parameter to restore the structure of the underground medium and describe the characteristics of the reservoir by migration imaging.It is also one of the key parameters of seismic data processing.It determines the accuracy of prestack depth migration imaging.Therefore,this paper takes the offset domain grid tomography as the main research object,and analyzes its application effect and influencing factors in the Dabei Research Area,which has important practical application value.In fact,the precision of the velocity model determines the accuracy of the migration imaging.If the velocity field is inaccurate,the spatial position error of the prestack depth migration imaging will be increased and the focusing precision will be reduced.Based on the sensitive characteristics of prestack depth migration for speed precision,the velocity field is modeled with prestack depth migration,and the quality of seismic imaging is used as the criterion to distinguish the precision of velocity field,and speed modeling is realized through the iterative process of velocity analysis-prestack imaging.This paper starts from the basic principle of the Kirchhoff integral prestack depth migration algorithm and uses the tomography method to build a velocity model: first,Kirchhoff prestack depth migration is performed on the seismic data,and picking up the residual time difference on the common offset point gather;secondly,using the residual time to calculate the amount of speed update,reconstructing the speed model as the next velocity model of the next migration imaging,continue to iterate to obtain the best imaging results;Finally,through the analysis of the application of the complex structure in the study area,it is proved that the tomography speed modeling method of this paper can get the high precision velocity field,which provides a practical method for other similar mountain complex structure speed modeling and mapping.