For seismic imaging in complex underground geological formations, currently themost effective process method is the use of prestack depth migration technology to achieve.Migration velocity accuracy directly affects the accuracy of migration imaging, therefore,to establish a more accurate velocity model to improve the precision of migration imagingis crucial. Prestack reverse time migration which makes use of the round-trip seismic waveequation is one of Prestack depth migration. It can reach high precision. It is not affectedby dip angle of reflection and can deal with the change of speed along vertical andhorizontal directions. In addition, it can perfectly process the rotary wave, multiple wave,prism wave. Prestack reverse time migration needs high precise velocity. Prestackmigration velocity analysis method makes use of ADCIGs to update the velocity and buildmodel. The ADCIGs extracted by one way wave equation migration are not stable in thesituation of steep dip angle. You see, reverse-time migration has no limitation by dip angleof reflection. We can get stable ADCIGs by extracting HADCIGs and VADCIGs fromreverse time migration. This angle domain commom image gathers velocity inversionmethod for pre-stack reverse time migration provide high-precision velocity field.Migration velocity analysis method combined with velocity analysis and migrationimaging. Velocity analysis results are more practical significance (imaging optimal), andthis kind of method has a lot, such as depth focus analysis, residual curvature analysis, andbased on Common Focus Point velocity analysis, especially the residual curvature methodhas been widely applied in industry. But extracting what kind of CIG is most conducive tothe velocity analysis, how to establish the right relationship with the residual moveout andresidual velocity and how to transform residual moveout or residual depth into thecorresponding velocity model correction. These are keys which affect such methodssuccessfully applied in complex area.First highlighted in this article are based on reverse-time migration in common angledomain imaging point gather extraction methods and principles, achieved angle domaingather based on reverse time migration, and demonstrated the superiority of angle-domaincommon-image gathers on handling multi-arrivals problems. When the geologic dips aresteep, the conventional way of computing common imaging gathers does not produceuseful geological angle information and it will cause artifacts. So this paper put forward atheory that through calculating the vertical angle domain common imaging point gather(Vadcig) and weighting with traditional angle domain common imaging point gather, to get the most optimized angle domain gather. We demonstrated the correctness and validity ofthis method through model trial. Underground medium is assumed horizontally layeredcase, we derived the residual depth equation from wave equation ODCIGs, then did slantstack, mapped to the formula ADCIGs the residual depth equation. Established relationshipbetween residual curvature and velocity perturbation, and update velocity through this. Forthe inherent noise in reverse time migration, we use the optimal filter method of Laplacian,and have achieved good results. |