Acoustic logging while drilling (LWD) technology plays a more and more important role in highly deviated angle and horizontal well logging due to 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, drilling bit and even tool mode waves. The flexural vibration transducer with a small volume and low resonant frequency is a good option for the acoustic logging tool. Meanwhile, it is difficult to directly use the simple piezoelectric bender in acoustic LWD tool because of narrow frequency band and other problems.

Researchers from the State Key Laboratory of Acoustics, Institute of Acoustics of the Chinese Academy of Sciences simulate a new typed receiver with cavity structure composed by a bi-laminated piezoelectric bender and a hollow cylindrical shell. The advantage is mainly embodied in small size and broad frequency band compared with the traditional simple piezoelectric bender. It proves that it is appropriate for receiving monopole waves on acoustic LWD tools.

The finite element method is used to calculate the vibration, admittance characteristics and receiving sensitivities, considering variables such as geometric sizes and loads in the simulation progress. Influences on receiving sensitivity are found in several parameters, including diameter and thickness of the bi-laminated bender, the volume of the cavity as well as the cavity open or closed. 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.

Fig. 1. Schematic diagram of acoustic LWD receiver (Image by WEI)

Fig. 2. Comparison of receiving sensitivities between open and closed cavity receivers (Image by WEI)

References: 

WEi Qian, CONG Jiansheng, WANG Xiuming. A Multi-modes Coupling Receiver for Acoustic Logging While Drilling.  Piezoelectricity, Acoustic Waves, and Device Applications (SPAWDA), 2014 Symposium on, ISBN 978-1-4799-6424-6, IEEE (pp. 90-93, Oct. 30 2014-Nov. 2, 2014, Beijing, China). DOI: 10.1109/SPAWDA.2014.6998533 

Contact: 
WEI Qian
Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China
E-mail: weiqian@mail.ioa.ac.cn