Research on attenuation rate correlation calibration method based on acoustic variable density logging.

In order to solve the problem of logging calibration without a free pipe in the process of acoustic variable density logging and the subjective problem of the free pipe calibration method, this paper studies an attenuation rate calibration method based on acoustic variable density logging. Using the developed acoustic wave probe response relationship device and the acoustic wave probe calibration device, the response consistency of the receiving probe of the acoustic wave instrument and the frequency of the transmitting probe can be calibrated in the laboratory, and the response consistency and frequency calibration coefficient can be obtained. Through this coefficient, the acoustic wave attenuation rate can be derived. After converting the acoustic wave attenuation rate into a relative sound amplitude, the scale coefficients of the well can be obtained. The relative acoustic amplitude of each measuring point in the well can be obtained by using the scale coefficient to evaluate the cementing quality. The acoustic variable density field test of 18 wells in the oilfield shows that the relative acoustic amplitude calculation results obtained by the attenuation rate correlation calibration method are basically consistent with the theoretical values, and the maximum deviation is 6.9%. The deviation is caused by the presence of ahead fluid in the outer annulus of the casing, the presence of trace bubbles in the casing, and the incomplete centering of the instrument. Compared with the traditional free pipe calibration method, the attenuation rate correlation calibration method innovatively replaces the free pipe calibration in the well with the indoor calibration of the acoustic instrument and solves the problem of acoustic variable density calibration when there is no free pipe in cementing quality logging. This method has better accuracy and a greater application range, which lays a foundation for the quantitative interpretation of acoustic variable density.