ngxuan Che

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, by 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 and effective electromechanical 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.

Research on sensitivity of dipole receiving transducers

The dipole receiving transducers play an important part in Cross-dipole array acoustic well logging tools. It is necessary to study the properties of the dipole receiving transducer, especially the sensitivity of it. In this paper, transducers in two ways of wiring, including parallel connection and series connection, were considered numerically and experimentally. The sensitivities obtained by numerical and experimental method respectively were contrasted. The results show that as a receiving transducer, the receiving sensitivity in series connection is higher, which can guide us in the dipole receiving transducer design. Keywords: dipole, receiving sensitivity, receiving transducer

Numerical study on the acoustic field in noncircular elastic pipes filled with fluid

Due to the high cost of real field test, the testing and calibration of acoustical logging tools are usually conducted in a steel pipe filled with fluid. The information provided by the calibration in a circular pipe is not proper for nonaxisymmetric dipole tools. So the possibility of using a noncircular pipe filled with fluid for the testing and calibration of acoustic dipole logging tools is considered. In our previous report the acoustic fields generated by a dipole source in the noncircular fluid waveguide with the rigid wall were numerically studied using the finite-element software package of Comsol Multiphysics. So called 2.5D method has been used. The transformed acoustic field in a frequency wave-number domain is calculated first and from which the acoustic field in the time space domain was obtained by a 2D Fourier transformation. In this report the method is extended to include an elastic wall instead of the rigid boundary of the fluid waveguide. The results show that the contribution of the elastic wall is significant to the whole acoustic field and the propagating modes in the waveguide are coupling of the modes in the fluid part with that in the elastic wall. Due to the high cost of real field test, the testing and calibration of acoustical logging tools are usually conducted in a steel pipe filled with fluid. The information provided by the calibration in a circular pipe is not proper for nonaxisymmetric dipole tools. So the possibility of using a noncircular pipe filled with fluid for the testing and calibration of acoustic dipole logging tools is considered. In our previous report the acoustic fields generated by a dipole source in the noncircular fluid waveguide with the rigid wall were numerically studied using the finite-element software package of Comsol Multiphysics. So called 2.5D method has been used. The transformed acoustic field in a frequency wave-number domain is calculated first and from which the acoustic field in the time space domain was obtained by a 2D Fourier transformation. In this report the method is extended to include an elastic wall instead of the rigid boundary of the fluid waveguide. The results show that the contribution of the e...

RESONANT FREQUENCY SHIFTS OF A FLUID FILLED CAVITY CAUSED BY A BUBBLE

In the previous studies for estimating acoustic wave velocities and attenuations of a rock specimen in a low frequency range using an acoustic resonance spectroscopy method, it was found that bubbles in a fluid filled cavity reduce the resonant frequency of the cavity significantly, which makes the measurement unstable. In this paper, this phenomenon is explained by using a simple model of a spherical fluid filled cavity with a single air bubble. It is pointed out that air bubble effects are caused by the vibration of the bubble coupled with the vibration of the cavity and, therefore, the measurement must be carefully prepared to prevent any air bubbles from entering the cavity.