高分辨率声波测井面临的问题及其对策

以减小接收探头间距为手段的高分辨率声波测井仪器已经在很多油田使用,但由此获得的测井曲线常常再现时差曲线“跳跃”及时差值不准的问题,特别是短源距声波测井仪器,该问题尤为突出。本文从井内声波传播的基本规律出发,发现在源距为1m附近,由于圆柱形井内声波波长与井径接近,声波在井内多次反射后,以地层纵波速度传播的声波具有一定的频散特征,从而导致声波的首波相位不固定,并随源距变化。这是目前高分辨率声波测井曲线“跳跃”的根本原因。为此我们设计了能够同时测量长、短源距声波波形并且长源距具有相控功能的阵列声波测井仪器,并开发了利用换能器波形计算声波测井频散曲线的方法。通过该方法可以充分利用波形的相位信息建立模型,得到无频散曲线,进而生成声波时差曲线。

Problems of high-resolution sonic log and counter-measures

The high-resolution sonic log instrument taking reducing the intervals of receiving probes as a tool is widely used in many oilfields, but it results in the problems of delta time "skip" on logging traces and inaccurate delta time values. These problems are more serious especially for the sonic log instruments with short source intervals. Starting from the basic regularity of sonic propagation in the holes, the paper discovered that when the source interval is about 1m,the sonic wave propagating with P-wave velocity of formation has some dispersion character after multiple reflection of sonic wave in the hole because of the wavelength of sonic wave in cylindrical hole approaching to the diameter of the hole,which leads to unfixed phases of head wave of sonic wave that change with source intervals. This is cardinal reason of "skip" on high-resolution sonic logging traces. For that reason,we designed array sonic log instrument that can simultaneously measure sonic waveform having long and short source intervals and have phase-control function for long source interval and developed themethod using waveform of transducer to calculate dispersion curves of sonic logging traces. It can fully utilize phase information of waveform to built up models by using the method and gain the dispersion-free curves, so that can further generate the delta time curves.