Enhancing VSP Imaging Quality by an Efficient Dip Filter Consistent with Velocity Model
Enhancing VSP Imaging Quality by an Efficient Dip Filter Consistent with Velocity Model
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DOI：
10.3997/2214-4609.201900698
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发表时间：
2019-06
期刊：
影响因子：
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通讯作者：
M. Lou;H. Simpson
中科院分区：
文献类型：
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作者：
M. Lou;H. Simpson
摘要VSP资料通常能提供比地面地震资料更高分辨率的地震图像，但由于VSP测量中井内接收器数量少且垂直固定，CDP褶皱低且不均匀，成像结果往往存在严重的偏移伪影。抑制VSP偏移伪影的常用方法是将偏移孔径减小到小角度。然而，小的孔径角可能无法对显著倾斜的结构成像。本文提出了一种与VSP偏移中的局部速度模型相一致的有效倾角滤波器，该滤波器既能保留真实的倾角结构，又能抑制偏移伪影。浸渍过滤器由两个主要部分组成：（1）我们首先基于由传统基尔霍夫偏移中的Eikonal解算器计算的走时表有效地计算从震源和接收器位置到每个图像点的波传播角，以及（2）然后，我们相应地基于由源和接收器传播的平分线定义的可能的倾角来对每个图像点执行倾角滤波与图像点的角度。模拟和实际VSP资料表明，与局部速度模型一致的倾角滤波器有效地提高了VSP成像质量。
Summary VSP data usually provides a higher resolution seismic image than surface seismic data, but its imaging result often suffers severe migration artifacts due to the fact that there are fewer, and vertically-fixed, borehole receivers and therefore low and uneven CDP folds in VSP survey. A common method to suppress VSP migration artifacts is to reduce migration aperture to a small angle. However, a small aperture angle can fail to image significantly dipping structures. Here, we develop an efficient dip filter consistent with the local velocity model in VSP migration, which preserves true dip structures and in the meantime suppresses migration artifacts. The dip filter consists of two major parts: (1) we first efficiently calculate the wave propagation angles from both source and receiver positions to each image point based on a travel time table computed by an Eikonal solver in conventional Kirchhoff migration, and (2) we then accordingly perform the dip filtering for each image point based on the possible dip angles defined by the bisects of the source and receiver propagation angles to the image point. Both synthetic and field VSP data demonstrate that the dip filter consistent with the local velocity model effectively enhances VSP imaging quality.