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Migration Velocity Analysis Of P- And S-waves Based On Elastic Kirchhoff Migration

Posted on:2012-04-01Degree:MasterType:Thesis
Country:ChinaCandidate:F LiFull Text:PDF
GTID:2120330338493472Subject:Solid earth material science
Abstract/Summary:PDF Full Text Request
Because the seismic wave-field is elastic, the waves propagated in the earth not only include P-waves, but also include S-waves and converted waves. To improve the reliability of the seismic imaging and describe the propagation of seismic wave-field more accurately, it is necessary to take full advantage of the vector characteristic of multi-component seismic data in the elastic imaging. However, as an important component of multi-component seismic processing, the great challenge of elastic wave imaging is the determination of migration velocity. Meanwhile, the efficiency and accuracy is a pair of contradictory in the process of migration velocity analysis. This paper considers these two important factors comprehensively and focuses on the study of migration velocity analysis of P- and S-waves based on the elastic Kirchhoff migration method.Based on the equations of multi-component Kirchhoff migration proposed by Kuo and Dai, through the rearrangement of the weight coefficients of PP- and PS-waves and the application of the unit polarization vectors at the image point, the 3D elastic Kirchhoff migration equations are derived and the 2D reduced form are provided. This Kirchhoff migration method operates directly on the vector wave-fields which removes a requirement for wave-fields separation in the preprocessing. The model tests show that this method is suitable for migration velocity analysis of P- and S-waves.As for the vector wave-?eld imaging, the elastic imaging condition can be extended to non-zero time and space shifts. In this paper, the method to extract the time-shift angle domain common image gathers and angle domain common image gathers of PP-waves and PS converted waves is established. First, by introducing the space-time-shift imaging condition to the elastic Kirchhoff migration equations derived in this paper, the time-shift offset domain common image gathers of PP-waves and PS converted waves are extracted. Then, the transformations of angle decomposition are performed to extract the time-shift angle domain common image gathers of PP-waves and PS converted waves. The space-shift imaging condition is the special case of space-time-shift imaging condition, the angle domain common image gathers of PP-waves and PS converted waves can be generated by this imaging condition.According to the characteristics of the reflective wave propagation kinematics in the angle domain, the residual depth equations of PP- and PS-waves which can be used for sloping layers are derived. These two equations are used for updating the velocities of P- and S-waves. The accuracy of migration velocity analysis is improved by taking full advantage of both the elastic wave image depth consistent principle and the flattening principle of angle domain common image gathers.The method proposed in this paper is tested on the Ken71 model, the Marmousi II model and the real filed data. The results show that this method can extract the angle domain common image gathers effectively and the updating migration velocities for both P-waves and S-waves are reasonable.
Keywords/Search Tags:Elastic Kirchhoff migration, Space-time-shift imaging condition, Angle domain common imaging gathers, Migration velocity analysis, Elastic waves image depth consistent principle
PDF Full Text Request
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