Abstract
In this article, a novel design of a piezoelectric dipole transducer is proposed for formation acoustic velocity measurement in the vicinity of a borehole with a frequency range of 0.4–6 kHz. The transducer which actuates a cylindrical shell to generate a pure dipole mode wave by using multiple piezoelectric bender bars is analyzed theoretically and simulated numerically by using the finite element method (FEM). Moreover, the transducer is fabricated and tested to compare with the numerical simulation results, which shows that the test and simulation results are in good agreement. Finally, compared with numerical simulation results of the traditional dipole transducer, it is shown that the proposed dipole transducer has higher transmitting sensitivities than commonly used ones, especially in low frequency responses. This work lays a foundation for the new development of the transducer in borehole dipole acoustic shear wave measurements. Especially, in a slow formation where the shear wave velocity is lower than that of compressional wave in the borehole fluid, the transducer could be used for highly efficient shear wave velocity measurements.
Highlights
Borehole acoustic wave logging or acoustic wave measurement is used to predict formation lithology, evaluate the formation porosity, and indicate the pore fluid properties in an open hole by measuring the compressional and shear velocities of the formation in the vicinity of a borehole [1]
In a slow formation in which the shear wave velocity is smaller than that of borehole fluid, borehole dipole acoustic measurement has been used for generating flexural mode waves propagating along the borehole, and these mode waves, during propagation, carry the shear wave events of the formation outside the borehole, and can be used for picking up the shear velocity of the formation [5]
In order to procure the accurate shear velocity and obtain the dispersion of flexural mode waves effectively, dipole transducers are required with a wide frequency bandwidth and a high radiation power
Summary
Borehole acoustic wave logging or acoustic wave measurement is used to predict formation lithology, evaluate the formation porosity, and indicate the pore fluid properties in an open hole by measuring the compressional and shear velocities of the formation in the vicinity of a borehole [1]. One of the most conventional, piezoelectric bender-type transducers [6,7,8,9], are extensively used in the borehole dipole acoustic measurement tools [10]. They have the disadvantage of limited bandwidth in low frequency [10,11].
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