P/PS Wave Velocity Inversion Of Obs Data Under3D Structure And Software Development

The unique geophysical characteristics of hydrate deposits offer the potential forthe application of seismic methods and techniques in the study of marine gas hydrates.The geophysical response of hydrate deposits to P and PS wave is entirely different.More accurate P/PS wave velocity becomes a strong basis for judging hydratereservoir. Being able to receive the P and PS wave in the meanwhile, OBS（OceanBottom Seismometers）becomes an effective tool for gas hydrate research.Conventional OBS velocity inversion is based on the Level Medium Inversiontheory. It means that doing the velocity analysis on the CMP gathers. This method issimple and feasible. However, it will cause large errors in more complex geologicalstructure. Peoples have done a lot of work on two-dimensional OBS velocityinversion. Liu(Liu,2009) developed the P/PS wave velocity inversion software basedon windows platform, which has achieved a better result in the research work.Yan(Yan,2010)ported it to Unix/Linux platform and realized the software system ofcross-platform. The main content of the paper is P/PS wave velocity inversion of OBSdata under3D structure and software development. Ensure the software running oncross platform, the programming used the C++, Qt and Open Inventor. Segmentalinteractive ray tracing method and whole-path interactive ray tracing method inthree-dimensional media are applied in the paper, which are based on Fermat’sprinciple and Snell’s Law. Both of the methods are fast in random interface velocitydistribution and the results are accurate enough. At the mean time, its precision can becontrolled according to requirement of ray-tracing. P/PS wave velocity inversion isbased on coherent inversion principle (Landa,1991). The optimum speed is measuredby the method of multi-channel cross-correlation.The former senior has completed a part of the work of the program design ofthree-dimensional OBS velocity inversion. But the right inversion result has not beenable to be got through the program, also the integrate inversion work of the P-waveand S-wave velocity cannot be completed. The paper has modified the incorrect partof the forward algorithm to make it adapt to the OBS inversion; Some kinds of coherent inversion algorithms have been added to the program to improve the basicprocess of the OBS velocity inversion; The database management of the software hasbeen improved to make the data shared successfully. The program truly realizes thehuman-computer interaction function of the velocity analysis and increases somerelative aided modular. The program truly realizes the visualization of the3Dgeological model. The operating interface of the software has been improved and thegraphic function has been modified. After the completeness of the paper, theOBSinversion3D software has realized the basic functions from data preparation,model building, velocity inversion of P/PS wave, analysis of human-computerinteraction to the output of result. The software also has been applied to the scientificresearch which is relevant to OBS and meets the demand of the scientific missionwell.