Walkaway VSP井旁各向异性速度模型反演方法

针对一个井源距VSP初至反演的井旁速度模型不能用于同一口井多个不同井源距VSP数据的偏移成像这一问题,本文介绍了一种使用Walkaway VSP的初至旅行时反演井旁各向异性模型的层速度和各向异性参数的方法。该方法根据声波测井速度的变化趋势对井旁一维速度模型进行分层,以零井源距VSP初至时间反演的速度作为初始速度模型,用一种接近沉积岩特性的多层各向异性介质模型描述和定义井旁速度模型的各向异性参数,利用不同井源距VSP的多条VSP初至时距曲线反演井旁水平层状各向异性速度模型的层速度和各向异性参数,得到Walkaway VSP偏移成像的井旁各向异性速度模型。把该模型用于Walkaway VSP实际数据的偏移成像处理,取得了较好的效果。

Inversion of walkaway VSP anisotropic velocity model near wells

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.