Jiansheng Cong

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.

A MULTI-MODES COUPLING RECEIVER FOR ACOUSTIC LOGGING WHILE DRILLING

Acoustic logging while drilling (LWD) technology plays a more and more important role in highly deviated angle and horizontal well logging due to the advantages such as high efficiency, low cost and etc. However, there still exist bottleneck problems because of the acoustic LWD environment in the borehole including noise of mud and drilling bit and even tool mode waves. Flexural vibration transducers with a small volume and low resonant frequency is a good option in acoustic logging tools. We presented a Helmholtz resonator receiver with multi-modes coupling with wide frequency band, high sensitivity and flat sensitivity curves than receivers with pure bending mode. The finite element method was used to calculate the vibration, admittance characteristics and receiving sensitivities. Considering variables such as geometric sizes in the simulation progress, optimized receiving sensitivity curve was finally obtained, with a maximum value of -195dB, and a fluctuation within ±5dB in the range of 10 to 20 kHz. It is appropriate for receiving monopole waves on acoustic LWD tools.

Numerical analyses on the sandwich dipole logging transducer with various loads

Numerical modeling for a sandwich dipole well logging transmitting transducer is conducted in this work. The characteristics for the first-order bending vibration of the sandwich transducer within different fluid loads are numerically analyzed. It is found that the resonant frequency and transmitting voltage response level are affected by the density, acoustic velocity and acoustic impedance of the fluid load. The numerical results were preliminarily validated by our experiment. The numerical analyses may provide useful suggestion for both the simulation design of logging transducer and the acoustic logging applications.

Performance analysis for acoustic well logging receivers

The structure of acoustic logging receivers can change their performance directly. In this article, impedance characteristics and receiving sensitivities of three kinds of acoustic logging receivers were numerically analyzed with the finite element method. The modeling results showed that: The piezoelectric tube transducer in radial vibration mode had higher receiving sensitivity in the frequency range of 8-20 kHz with some ups and downs, while its sensitivity changed great below 5 kHz. The laminated circles transducer in bending vibration mode had higher sensitivity and better flatness below 4 kHz, but its sensitivity and flatness changed lower from 8 kHz to 20 kHz. The rectangular laminated piezoelectric transducer in the length stretching mode had better flatness below 20 kHz. In addition, acoustic well logging receivers in the future will have higher sensitivity, wider frequency bandwidth and smaller volume, which was pointed out in the article.

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 analysis on the acoustic well logging transducers with various fluid load

It is numerically analyzed how the acoustic attributions of monopole well logging transducer change when excited in different fluid load media, such as water, silicone oil and mud with different components. The logging transducer is a radially polarized piezoelectric cylindrical tube with both ends shielded, being used as either transmitter or receiver. For the radially resonant mode of the transducer, the resonant frequency, transmitting voltage response and receiving sensitivity of the transducer are affected by the medium density and velocity. When the medium density is constant, the resonant frequency and the transmitting voltage response increase with the increasing of medium velocity, while the receiving sensitivity decrease with the increasing of medium velocity. When the medium velocity is constant, the resonant frequency decrease with the increasing of medium density, while the transmitting voltage response and receiving sensitivity increase with the increasing of medium density. For the given ac...