Inversion of walkaway VSP anisotropic velocity model near wells
Hou Aiyuan1,2, Geng Weifeng2, Zhang Wenbo2
1. College of Marine Geo-sciences, Ocean University of China, Qingdao, Shandong 266100, China;
2. Geophysical Research and Development Centre, BGP Inc., CNPC, Zhuozhou, Hebei 072750, China
Abstract:Velocity model inversed from VSP first-breaks at an offset in a well is not suitable for VSP migration imaging at different offsets in the same well. To solve this problem we propose in this paper an approach to inverse velocity and anisotropic parameters of a model near well using walkaway VSP first-breaks. First, based on well-log acoustic velocity, an 1D velocity model is divided into a certain number of layers. Then velocity inversed from VSP first-breaks at zero offset is taken as the initial velocity model. After that, anisotropic parameters of velocity model near the well are described and defined by multi-layered anisotropic model close to sedimentary rock. Finally, VSP first-breaks at different offsets are used to inverse velocity and anisotropic parameters of horizontal layered model near the well to obtain anisotropic velocity model that can be applied to walkaway VSP migration. The proposed approach achieves good results in real walkaway VSP data migration.
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