3D3C VSP imaging technology based on scattering time-distance relationship
YAN Yuanyuan1, QIN Li2, LUO Kun2, LU Jun1, WANG Yun1
1. School of Geophysics and Information Technology, China University of Geosciences (Beijing), Beijing 100083, China; 2. Southwest Branch, BGP Inc., CNPC, Chengdu, Sichuan 610213, China
Abstract:Acquired by special recording geometry, 3D3C (three-dimensional and three-component) VSP data can't be processed by conventional processing methods for surface seismic data. In addition, there are less applicable 3D3C-VSP imaging technologies with high precision, and there is less processing software for 3D3C-VSP data. To process 3D3C-VSP data, many iterations should be run for velocity analysis, and it is very difficult to get 3D imaging results. In this paper, we propose a method for velocity analysis and migration for 3D3C-VSP data. It is based on wave scattering theory and without iterating. First, we set up the time-distance curve equation of reflected wave in VSP data. Based on this equation, we move the amplitude at each time sample of the seismic trace to the corresponding reflective surface and extract the common-imaging-point gathers by interference stacking. Then, for the asymmetric ray-paths and inconsistent migration velocities of up-going and down-going waves, we convert the NMO corrected up-going waves in common-imaging-point gathers to virtual offset gathers with the characteristics of hyperbolic time difference. Eventually, through velocity analysis and NMO correction for the virtual offset gathers, we obtain high-precision PP and PS wave imaging profiles. This method was applied to the 3D3C-VSP seismic data of Well A in Sichuan Basin, and produced better imaging results than the conventional VSP-CDP stacking method.
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