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研究了应用低频超声垂直入射反射波实现套管-水泥界面流体微间隙薄层厚度的反演方法。应用灵敏度函数比较分析了分层系统反射谱各阶谐振频率处的相位跳变量较之各阶谐振频率作为反演特征量的优势。通过目标函数分析,选取分层系统3~10阶谐振频率处相位跳变量作为特征量,利用BP神经网络实验获得0.1~1.0 mm内不同间隙层厚度的反演结果。反演结果与真实值的平均相对误差为4.6%,最小反演厚度仅为波长的18%。所选取的相位特征量也可用于其它层状高声阻抗介质下的薄层厚度反演。
In this paper, the method of inversion of the microcosmic layer thickness of the casing-cement interface fluid by using the low frequency ultrasonic vertical incident reflected wave is studied. By using the sensitivity function, the phase jumps at different resonant frequencies of the hierarchical reflection system are compared and analyzed. Through the analysis of objective functions, the phase jumps of the third to tenth order harmonic frequencies of the stratified system are selected as the feature quantities, and the inversion results of the thickness of different gap layers within 0.1 ~ 1.0 mm are obtained by BP neural network experiment. The average relative error between the inversion result and the true value is 4.6%, and the minimum inversion thickness is only 18% of the wavelength. The selected phase features can also be used for the inversion of the thickness of the thin layer under other layered high-acoustic impedance media.