3D VSP Wave Field Separation And Imaging

With the development of exploration and boreholl seismic, the research and application of 3D VSP technology is progressing rapidly.As the multiple detector work in the well and surface source is various, the wave field in 3D VSP is more complicated. In different gather, wave field distribution and energy distribution of different wave such as P-P wave and P-SV wave is different. It is necessary to research time-distance equation and theoretical model of different wave before wave field separation.Polarization filtering is one of the most frequently used methods in wave field separation of three-component VSP. It is similar to single trace process (one shot point and one receiver) and can be applied mechanically in 3D VSP. But as total traces are so much and offset is so various that it is necessary to improve the calculation of polarizing angle and fixed coordinate system. To study realization of polarization filtering and analysis application condition of the method of polarization filtering, this paper indicates that conventional method can only separate the main energy of downgoing P-P wave field and upgoing P-SV wave field and downgoing P-SV wave field. Usually affected by observe angle, the separation effect of conventional method needs to be improved. Then this paper studies the computational method of polarization angle and decreases the ambiguity by inducting space derivation as additional condition.The polarization method of float coordinate system is advanced relative to fix coordinate system. Conventional method is based on the direction of propagation of direct wave, but doesn't aim at the upgoing wave we concerned. For any reflective spot of subsurface, Method of float coordinate system builds the coordinate system by the main energy orientation of the reflected wave. Coordinate system is different for difference spot. This method is totally based as the wave field we concerned, and it can realize the optimum separation. Imaging is one of the key technologies in 3D VSP data processing. At present, the high quality imaging method is scarce, conventional VSP-CDP transfer approach or Kirchhoff integral method is still used in imaging. Wave equation imaging method has higher accuracy and better amplitude preservation than conventional methods, and its core problem is wave field extrapolation operator. In general, it requires that the operator, in addition to providing high computational efficiency, shall be adaptable for steep dip reflective imaging and much rough alternation of transverse velocity. By building the wave field extrapolation operator by 3D VSP wave equation, this paper studies 3D VSP wave equation imaging method of small scale geologic body, and further analyzes the amplitude preservation of 3D VSP wave equation imaging.The research of this paper is based on 3DVSP actual data in Ken71 area. In view of characteristics of actual data, we adopt initiative thinking and approaches. The results of processing are substantially better than the VSP-CDP and Kirchhoff migration.