Velocity Analysis Of Multi-component Seismic Data In Depth Domain

Prestack depth migration can precisely image the complicated geologicalstructures, and elastic wave depth migration may effectively reduce the ambiguity ofP-wave exploration. The key of prestack depth migration is high-resolution velocitymodel. However, the present methods of elastic wave velocity analysis can not meetthe demand of prestack depth migration. Therefore, a high-resolution velocity analysismethod needs to be reestablished urgently. For this purpose, we perform the researchon elastic wave depth velocity analysis and depth-domain layers matching as follows:Since prestack depth migration is highly sensitive to velocity model, migrationvelocity analysis can be performed according to migration error so as to establishP-wave velocity field. Migration velocity analysis is carried out in common imaginggathers. In this paper common imaging gathers are formed by Kirchhoff prestackdepth migration. We formulated the velocity updating equations in P-wave commonimaging gather, and performed prestack depth migration analysis on P-wave prestackseismic data according to the flattening criterion for common imaging gather.Adopting layer stripping method for velocity analysis from top layer to bottom layer,constraining update by geological layers, we finally established the depth-domainP-wave velocity field for the prestack depth migration.The ordinary converted wave velocity analysis methods in common convertedpoint gathers can cause great accumulation error and are low precision. We proposeda high efficient and precise method for converted wave velocity. Based on scatteringtheory and wave-field characteristic of scattering wave, velocity analysis and timemigration imaging are carried out in the improved equivalent offset common scatterpoint gathers where the formation of converted-wave common scatter point gathersand imaging are independent on any P-wave information. Performing depth mappingfor elastic wave time imaging section, picking interlayer Vp/Vs ratio, and convertingit into depth domain integrating P-wave velocity field and P-wave depth imagingsection, we finally established the S-wave velocity field with high precision.If there is miner error in velocity field, the phenomenon of depth nonconformity will exist in the elastic wave depth imaging section of field seismic data, which meanswe need layers matching. We formulated the layers matching equations for updatingS-wave velocity model, which can make elastic wave imaging satisfies the depthconsistent principle for multi-wave joint interpretation.The elastic wave prestack depth migration velocity analysis is performed inhorizontal layers model, relief model, depression model and field data, the resultsindicate that combining P-wave Kirchhoff integration prestack depth migrationvelocity analysis, ratio analysis method of converted-wave velocity analysis based onequivalent offset common scatter point gathers and elastic wave depth-domain layermatching method can obtain P-wave and S-wave velocity field with high precision,which can meet the velocity field demand for elastic wave prestack depth migration.