套管井声场合成波形及其时频特征分析

数值计算了点声源激励下套管井声场的声压波形。计算模型包括了实际中所有的三类岩石及两个界面的各种胶结情况,声源频率采用实际的测井频率。对合成波形进行了基于Wigner-Ville分布的时频分析。计算和分析结果说明,波列中的套管波、伪瑞利波在一、二界面不同的胶结情况下有明显的变化规律。二界面未胶结时,套管波模式的时频分布随管外水泥层厚度的变化而变化。它们与地层体波成分的特征可作为管外水泥胶结质量评价的重要依据;而中速地层时地层体波能量最强,有利于胶结质量评价。

Synthetic waveforms of the acoustic field in cased boreholes and their time-frequency distribution

Synthetic acoustic pressure waveforms of the acoustic field excited by a point source in cased boreholes are calculated. All three kinds of lithology in field and various cement bonding cases for the two interfaces outside the steel casing are considered. The center frequency of acoustic source used in calculation is the same with the logging tools used in field. The time-frequency analysis based on Wigner-Ville distribution is used to synthetic waveforms. The obvious varied regularities of the casing arrivals and the pseudo-Rayleigh waves can be observed in waveforms and time-frequency distribution when the bonding conditions of the two interfaces change. The time-frequency distribution changes along with the changing of the thickness of cement layer when the cement and formation is not bonded. These characteristics and the characteristic of formation body waves can be used as an important basis for the evaluation of cement bonding quality outside the steel casing. The formation body waves in the formation with medium velocity have the biggest energy among the all three kinds of lithology, it's advantageous to the evaluation of cement bonded quality.