The Application Research Of Pre-stack Depth Migration Technique

Normal seismic data processing usually uses post-stack migration ,however, it just canmake reflecting layers return its own position and make coiling wave converge and can't dealwith uncommon reflecting points stacking of inclining interfaces .The pre-stack migrationtechnique is one of the effective methods in solving fine velocity analysis and complexstructures imaging, at the same time it is also the development tendence of seismic dataimaging in our country or overseas in recent years. Pre-stack migration is also the keytechnique in solving seismic data imaging in complex areas where the velocity vary rapidly .The paper firstly introduce the basic conception of migration and its developmenthistory .According to these development phases of migration ,it introduce the basic principleand achieving methods of migration.The paper places the emphasis in the sample of a 3D prospect in Jiuquan basinKulongshan contradictory covering and overturning structure , through GeoDepth pre-stackmigration software introducing 3D pre-stack migration principle ,its achievement steps and itsimaging effect .The task require us to find out fault character of Kulongshan contradictorarycovering and overturning zoster and make broken points clearer and make objective layersmore reliable to be easily traced. According to data character ,we divide the process into timefield and depth field .The difficulty of data time process is : suppressing regular disturbanceand attenuating random disturbance;compensating pre-stack energy and frequency;velocityanalysis;calculating static correlations;right stacking and imaging ,accurate migration andreturn its position. According to the character of original data and the difficulty of theprocessing and the processing requirement of the geological task and the key things to bedealed with ,we adopt corresponding technique measurement. The key steps in depth field is :the first one is founding the structure model in time field;the second one is founding originalvelocity model;the third one is optimizing the velocity model. Comparing and analyzing thetime section with post-depth migration section, we can realize that there are someimprovement in depth migration section than time section and representing in these aspects:the first one is that the structure shape of depth migration is relatively integral and reflectingS/N improves;the second is that stratum contact relation is more clearer after pre-stack depthmigration;The third one is that there are also some improvement in imaging in deep andshallow stratum and that wave group character is preferable and that its frequency straps arewider and that the resolution improves and that swing fidelity is higher. The shortcoming isthat the imaging effect isn't perfect because the objective layer of pre-stack depth migration isvery deep and its S/N is very low. At the same time migration drawing arc phenomena can'tbe suppressed enough in some places.