In vertical seismic profiling (VSP) exploration, it is difficult to produce an accurate image for large-offset reflections only using reflection waves and the image resolution is low in traditional VSP-CDP stacking as is the number of folds of reflection points. To mitigate these problems, we present an inverse Gaussian beam stacking method for imaging both primary reflections and free-surface multiples. We first compute the stacking weighted functions at each trace location by Gaussian beam forward modeling, and then apply an inverse projection for VSP data to produce common shot gathers (CRP). Since inverse Gaussian beam stacking maps the common-shot data along finite-frequency wave-paths instead of single rays as the traditional ray-based stacking method does, it enlarges the reflection-point coverage, increases stacking fold and reduces the requirement for large bin sizes. We incorporate free-surface multiples into the proposed inverse Gaussian beam stacking, which enables us to expand the horizontal imaging aperture and mitigate the low-fold problem of primary reflections in the shallow large-offset regions for VSP surveys. Numerical examples for synthetic and field data demonstrate the feasibility and adaptability of the proposed inverse Gaussian beam stacking method for VSP data.

中文翻译：

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逆高斯光束叠加方法在二维VSP中成像主反射和自由表面倍数

在垂直地震剖面（VSP）勘探中，仅使用反射波很难为大偏移量的反射生成准确的图像，并且在传统的VSP-CDP堆叠中，图像分辨率低，反射点的折数也很多。为了缓解这些问题，我们提出了一种反高斯光束叠加方法，用于对主反射和自由表面倍数进行成像。我们首先通过高斯束前向建模计算每个迹线位置处的堆叠加权函数，然后对VSP数据应用反投影以生成公共镜头集（CRP）。由于高斯逆光束叠加将共同发射的数据映射到有限频率的波径上，而不是像传统的基于射线的叠加方法那样沿单一光线进行映射，因此扩大了反射点的覆盖范围，增加了堆放折叠数并减少了对大尺寸垃圾箱的需求。我们将自由表面倍数纳入拟议的反高斯光束叠加中，这使我们能够扩大水平成像孔径并减轻浅层大偏移量区域用于VSP测量的一次反射的低折问题。合成和现场数据的数值例子说明了针对VSP数据提出的逆高斯光束叠加方法的可行性和适应性。