阵列声波测井时差拾取的慢度距离相关-SDC法

The application of slowness distance coherence-SDC on array acoustic logging slowness pickup

对于阵列声波测井多个接收器声波波形数据,提出了时差拾取的慢度距离相关-SDC法.其核心思想是阵列声波信号在均质地层中,模式波到达时间和接收器到发射器距离成线性关系,原点到各个模式的距离是不变的,因此在拾取时差中引入Hough变换,而波形识别采用相关性算法.具体是首先选取阵列声波其中一个信号和其余信号做STC,其次把相关系数以时间轴叠加得到时差-距离曲线,最后采用二维Hough变换得到慢度距离相关-SDC图来拾取时差.给出了慢度在Hough空间的计算公式.将Hough空间按照纵波、横波、斯通利波特征分区和采用增强的变换处理办法后,测试了在一段阵列声波测井资料处理中的应用效果.对比分析了三维Hough变换和二维Hough变换、STC和SDC的在应用中的区别,证明了SDC是多个接收器STC方法的一种发展.

In term of array acoutic logging waveforms,this paper forwards a new method on slowness pickup,which bases on the principle that compressional wave,shear wave and stoneley wave arriving time linearly increase with receiver-emitter distance in homogeneous formation,so combining correlation algorithm and Hough transform could identify waveforms and then pickup slownesses,and which is defined as slowness distance coherence-SDC.Two waveforms create a STC plot,so N array aoustic data could create C2N-1 STC plots.Merging all STC plots into a plot is not a easy job for each STC has different delta time,while same waves have same distance to origin in the homogeous formation,and compressional wave,shear wave and stoneley wave have different distance to origin.So using ＂distance＂ identify different wave don＇t care delta time changing or delta distance changing.SDC firstly chooses an array acoutic signal of one receiver and correlates with other receivers＇ signal,so N-1 slowness time coherence plots could be calculated if tool has N receivers.The second step is stacking each slowness time coherence plot by signal time,so each plot could convert to a correlation coefficients curve with delta time axis,and N-1 correlation coefficients curves are present now.N-1 correlation coefficents curves is a 2-dimension coeffient plot of delta time versus receivers＇ distance,and compresional wave,shear wave and stoneley wave are three lines relationship on this plot in homogeneous formation.As Hough transform has the advantage of lines identifcation,so line Hough transform is applied on three wave identication by waves＇ linear feature.Finally,transforming of 2-dimension coefficent plot get a new plot,which x-axis is slowness and y-axis is distance.Compressional wave,shear wave and stoneley have three peaks on STC,and they also have three peaks on SDC plot.Therefore,three slownesses are pickuped by their peaks.The Hough trandform idea is also applied in the high resolution slowness pickup instead of simple merging of several STC.Slowness calculating equation in Hough space is derivated and given in this paper.The Hough space has different partations of compressional wave,shear wave and stoneley wave,so enhanced method is suggested in the processing,furthermore,a short interval log data is processed and verifying SDC result with other software.At end of this paper compares different wave identification methods,3-D Hough transform and 2-D Hough transform,STC and SDC in the applications.SDC is a development of STC in the array acoustic slowness pickup.