纵波速度径向层析成像分析

Analysis of radial detection characteristics of compressional waves

钻井会造成近井壁附近岩石的声学性质改变,为研究纵波径向探测特性,本文使用径向柱状分层模型,应用二维轴对称有限差分法详细考察了过渡带厚度、声源频率以及接收器源距变化下,单极子测井响应的变化特征,并采用慢度-时间相关法研究了不同条件下所测量到的声速变化。最后基于射线理论,分析了不同条件下的首波到时变化特征。基于地层速度逐渐增加的模型表明,纵波的径向探测特性受源距影响较大,通过不同源距信号的组合,可以实现对近井壁纵波速度进行层析成像。

Drilling causes variation of the rock properties in the vicinity of a wellbore.In this article,we use the radial cylindrical layered model to examine monopole logging response with a two-dimensional axisymmetric finite difference method.Three variables are set,and they are the transition zone thickness,the source frequency and source-receiver spacing,respectively.We also use the slowness-time correlation-method to evaluate sound speed variations under different conditions.At last,based on the ray theory,the variation characteristics of the arrival time of the first wave under different conditions are analyzed.Based on a model of increasing formation velocity,we conclude that the radial detection characteristics of compressional waves are greatly influenced by spacing.By combining different signals with various spacings,it is possible to obtain the tomography of the compressional wave velocities near wellbore.