Ultrasonic echo constrained inversion method for acoustic impedance of medium on both sides of the casing pipe

In the process of oil exploration, it is important to accurately evaluate the quality of the cement bond in the annular region between the rock layer and the casing pipe. The traditional ultrasonic pulse echo signal processing technology is based on the characteristic analysis of resonance wave amplitude or group delay curve. Since the resonance wave amplitude and group delay characteristics are easily affected by the fluid in the casing pipe, it is necessary to choose the ultrasonic signal of the free pipe casing for calibration, so it is greatly limited in the application. According to the different response characteristics of ultrasonic echo signal in time domain to the acoustic impedance of the inner and outer medium of the casing pipe, a constrained inversion method of ultrasonic echo signal is proposed in this paper, and ultrasonic experiments are carried out. A total of 12 cases are measured for 2 specifications of casing pipe and 6 combinations of internal and external acoustic impedance. Finally,the proposed constraint inversion method is applied to process the measured echo signal, and the acoustic impedance of the medium on both sides of the pipe is obtained, and the results are consistent with the actual parameters.