Experimental Study on the Receiving Piezoelectric Vibrator of Azimuthal Acoustic Logging

Abstract

The performance of the azimuthal receiving piezoelectric vibrator has a major impact on the azimuthal acoustic logging tool. The evaluation of the performance and selective preference of piezoelectric vibrators through experimental methods will help improve the measurement accuracy of the tool. A heating tester was developed to test the static capacitance, resonant frequency, admittance and receiving amplitude of the vibrator at different temperatures. Far-field underwater acoustic tests were used to analyse the peak-to-peak amplitude, sensitivity and −3 dB angle of the vibrator and to determine the amplitude correction coefficients of each vibrator. The horizontal directivity of the azimuthally receiving phased subarray was also tested. Compared with the values at room temperature, the resonant frequency of the piezoelectric vibrator decreases by 9.20%, the static capacitance increases by 21.33% and the amplitude increases by 5.29% at a high temperature of 155°C. The underwater acoustic test showed that the main lobe of the receiving directional characteristic of the vibrator is symmetrical along the 0° main maximum direction, the −3 dB angle of the main lobe is 115°–142° and the average sensitivity level is −209.38 dB. The −3 dB angle of the receiving subarray is 66° and 60° without and with phase delay, respectively, and the energy of the received waveform is significantly increased. The piezoelectric vibrator can function stably at high temperatures, and its performance can be recovered after heating. It has good azimuthal resolution and high sensitivity, but the amplitude response has some discretion which needs to be corrected.