超声反射法套管-地层环空间介质波阻抗反演方法与成像实例

针对套管井反射式超声波水泥固井质量检测问题，本文利用超声反射波频谱中套管共振透射窗内的复合反射系数，提出了定量反演套管-地层环空间内介质的波阻抗的方法. 利用复合反射系数中多个频率点的相移反正切函数主值，给出了波阻抗的计算公式，并把套管-地层环空间介质中波的相移的整、实特性作为波阻抗反演收敛的判据. 针对井下实际测井环境中超声换能器性能受温度和压力等的影响而发生变化，导致的声源波形（子波）和复合反射系数不确定的困难，提出了用井下原地（in situ）实测波形定量估计声源波形和复合反射系数的方法. 通过对合成数据的处理，分别考察了已知介质的声学和几何参数存在的偏差对套管-地层环空间内介质的波阻抗反演结果的影响. 本文对多组模型井检验数据进行了目的层介质的波阻抗反演与成像，成像结果与真实情况吻合，验证了反演方法的有效性. 最后对现场实测资料进行了套管-地层环空间内介质的波阻抗定量反演与成像.

A wave impedance inversion method and practical image examples of the medium in the annulus space between the casing and the formation utilizing reflected ultrasonic waves

We propose a wave impedance inversion method of the medium in the annulus space between the casing and the formation utilizing the compound reflected coefficients within the window of resonant transmission frequency of the casing in frequency domain. Calculating formula of wave impedance is obtained by main values of the inverse tangent function of phase_shift at two neighboring frequencies and the corresponding integral character of phase_shift is denoted as the convergent criterion of wave impedance inversion. To solve difficulty of the uncertain acoustic source waveforms and the compound reflected coefficients caused by ultrasonic transducer that is affected by temperature and pressure in downhole casing, the theoretical method of obtaining acoustic source waveforms and compound reflected coefficients from in situ ultrasonic echoes are developed. With processing of synthetic data, the effects on wave impedance inversion results of the medium in the annulus space between the casing and the formation are investigated as the known acoustic and geometrical parameters deviate from the corresponding exact values. The validity of the inversion method is verified by good agreement between the distribution status of the practical medium and wave impedance inversion images after wave impedance images of the data in two scale wells are obtained. Wave impedance inversion and imaging of the medium between the casing and the formation based on the practical data of an oil field are carried out.