Study Of The Converted Wave Pre-Stack Time Imaging By Pseudo-offset Migration

Seismic wave imaging is important in the exploration of resources. It can generateaccurate imaging of the underground geological formations by migrating the reflected ordiffracted wave to the underground locations where they appear. Comparing with thecompressional wave exploration, the shear wave exploration has many advantages. It cansupply us much more information about the target. But there is still some limitation to useshear wave to do the exploration. It costs a lot. High quality shear wave data is also difficultto obtain. Considering those, here is a more practical and more economical method, which isusing the converted wave to replace the shear wave. Converted wave exploration is moreuseful, for example in the process of the structure imaging, the lithology analysis, the fluididentification and monitoring the reservoir. Because the study and process of converted wavedata have its own complexity and particularity, for example, the calculating of the wave fieldseparation speed and the migration imaging. In this way, this method can cover the shortagesof the compressional wave exploration. The converted wave migration imaging is one of themost important steps.Based on the fundamental theory of the pre-stacking time migration, this thesis hasrealized two converted wave pre-stacking time migration methods, which are EquivalentOffset Migration (EOM) and Pseudo Offset Migration (POM). By comparing the twomethods, the author has understood more thoroughly about the converted wave pre-stackingtime migration theory. The POM comes out from the EOM, but they have different mappingmodes. In order to make the EOM gathers are hyperbola, the EOM puts the shot and receiverat the same point. It is suitable to conventional velocity analysis. However, its ray parametersare uncertain. The ray path of the POM is in accord with the Snell Law, so in this way it cangive us the true common reflection point gathers. The author has compiled two programs toextract gathers for EOM and POM respectively. Five models, which are upheaval model,deboss model, faults group model and vein model, have been designed to test the twomethods. After comparing POM with EOM, it shows that EOM method relies on the initialvelocity more than the POM method. The POM method is not sensitive to the initial velocity. POM is better than EOM at the imaging of the interface with large dip.