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Migration Velocity Analysis Of Elastic Vecterial Wavefield

Posted on:2010-01-27Degree:MasterType:Thesis
Country:ChinaCandidate:B HouFull Text:PDF
GTID:2120360278460849Subject:Earth Exploration and Information Technology
Abstract/Summary:PDF Full Text Request
As an important step of multi-component seismic data process, elastic seismic migration is a significant improvment to traditional seismic data migration. Based on elastic wave equation, elastic seismic migration may describe earth media more precisely. Except for migration method, migration velocity is also a key factor of migration. In order to develop seismic migration image, we should do some research work on migration velocity analysis and velocity model construction. So, the studies are as follows:A strategy of seismic first break traveltime calculation with the finite difference method is proposed in this paper firstly. The traveltime calculation can adapt to the medium that velocity varies strongly in vertical and horizontal orientation based on expanding wavefront method. The dichotomy is employed in looking for the location of wavefront point. Thus, the algorith of first break traveltime calculation is improved, and its stability and precision are enhanced too. The method is applied successfully with the complicated model data and demonstrates it's effectiveness.Based on Kuo and Dai's vectorial wavefield extrapolation equations, the Kirchhoff migration equations are derived by means of introducing unit vectors, which represent the ray directions at the imaging points of the reflected P-wave and PS converted wave in this paper. Furthermore, using the slope of the events on shot records and ray racing procedure, the specular reflection points are found and the reflection data are smeared along the Fresnel zone. Migration method proposed in this paper can solve two troublesome problems of migration arcs effectively caused by limited aperture receiving and imaging artifacts resulted from wave propagation at the velocity of non original wave type effectively. The migration method is applied successfully with the model data, which demonstrates the new method is effective and correct.Based on elastic Kirchhoff migration of shot gather, multi-wave angle domain common image gathers are proposed in this paper. Introducing space shift image condition into elastic Kirchhoff migration, we obtain general integral elastic Kirchhoff migration equations. Implementing general integral elastic Kirchhoff to prestack data of shot gathers, multi-wave local offset domain common image gathers are extracted. Afterwards, transforming radial traces to local offset domain common image gathers in Fourier domain, we can obtain P-wave incidence angle domain common image gathers of PP wave and P-wave incidence angle domain common image gathers of PS converted wave.Velocity-updating equations of P-wave incidence angle domain common image gathers of PP wave and PS converted wave are derived respectively in this paper. We expand the criterions of migration velocity analysis of angle domain common image gathers which is based on the acoustic theory and obtain multi-wave the criterions of migration velocity analysis of angle domain common image gathers. Based on the theory above, we apply the migration velocity analysis to fualt model, Ken71 thin layer model and the field multicomponent data. The results demonstrate that migration velocity analysis method based on multi-wave angle domain common image gathers which are proposed in this paper is effective.
Keywords/Search Tags:travel-time, elastic Kirchhoff migration, migration velocity analysis, PS converted wave, angle domain common image gathers
PDF Full Text Request
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