Optimization Design for the Sandwich Piezoelectric Transmitters in Acoustic Logging

An optimized transducer prototype with a sandwich structure vibrated longitudinally is proposed for a transmitter in acoustic logging, especially in acoustic logging while drilling, 5y taking account of drilling environments with high temperature and pressure, as well as strong collar drilling vibration during the drilling process. Aimed to improve the transmitting performance, numerical and experimental studies for the transducer optimization are conducted. The impact of location and length of the piezoelectric stack on resonance characteristics arid effective electromeehanical coupling coefficient is calculated and analyzed. Admittance and transmitting performance of the proposed transducer are measured in laboratory experiments, and the results are compared with simulated ones. It is shown that the newly proposed transducer has higher transmitting performance with lower resonance frequencies. This work provides theoretical and experimental bases for transducer designing and acoustic wave measurements in acoustic logging, especially in acoustic logging while drilling.

Experimental studies of linear phased-array transmitter acoustic logging in cased wells with scaled borehole models

Laboratory cased-hole acoustic logging simulations are developed with the linear phased-array transmitter in scaled cased well models for evaluating the feasibility of extracting formation acoustic parameters through casing.The full waveforms are measured with different cement bonding models.By analyzing the measured wavetrains and the time-slowness correlation graphs,it is showed that when the generation conditions of the refracted compressional wave and the refracted shear wave are reached successively by regulating the direction of acoustic beam radiated from the linear phased-array transmitter,steered angle of the main radiation lobe with both good bonding interfaces.The refracted compressional wave and the refracted shear wave can be stimulated obviously and the casing wave can be suppressed effectively,even when the casing and cement（or the cement and formation） is not bonded.Based on these observations, it is worthwhile to apply the linear phased-array transmitter to determine formation velocities,particularly in poorly bonded cased well.The works establish the experimental and theoretical foundation for new generation cased-hole acoustic logging tool development.