Simulation And Design Of Small Size Dipole Acoustic Logging Transducer

In recent years,significant progress has been made in unconventional oil and gas exploration.The exploration and development of unconventional shale reservoirs often uses highly deviated wells or horizontal wells.The through-drill pipe sonic logging technology is not limited by horizontal displacement and well conditions,so it is very good in unconventional shale reservoir evaluation,perforation and fracturing evaluation,oil production effect evaluation,and production optimization design.However,due to drill pipe size constraints,it is difficult for conventional-sized logging tools to reach the target layer.At the same time,the dipole shear wave far detection technology has achieved good application results in the exploration of fracture-cavity oil and gas fields.The ultra-deep reservoirs of the Tarim Basin have become the key areas of exploration because they contain such reservoirs.The wellbore structure shows that the drilling has been repeated many times.As the borehole diameter becomes smaller,it is difficult for conventional-sized logging tools to meet the measurement requirements.Therefore,it is of great significance to design sonic logging transducers that are suitable for working in small boreholes.This paper is based on a thin dipole transducer,comprehensively considers the dynamic system and electrical system of piezoelectric materials,and uses the multiphysics module of ANSYS simulation software to simulate the transducer.The first part is based on the formation properties and borehole conditions.For the performance requirements of the dipole piezoelectric transducer,the length,thickness,relative area ratio of the piezoelectric crystal of the piezoelectric transducer and the metal substrate and the connection relationship between the metal substrate and the fixed frame are analyzed.Then,according to the influencing factors,a dipole sound source that meets the requirements for detection in the slim hole is optimized and analyzed,and the horizontal directivity of the sound source in the infinite water area is simulated and analyzed;the second part is processed according to the optimized design size The actual transducer substrate,and the four piezoelectric transducer substrates are installed and fixed on the frame according to the result of structural optimization.The impedance analyzer and the underwater acoustic test system were used to test the actual performance of the transducer,which provided the basis for the next step in the well test of the small-sized dipole transducer.The resonant frequency of a dipole transducer must be lower than the cutoff frequency of the dipole bending wave in the target formation in order to excite the high SNR signal.Based on the design requirements of the small size and low resonant frequency of the transducer,the relationship between the resonant frequency and the size and structure of the small-size dipole transducer is studied in this paper.The structural parameters of the piezoelectric crystal in the thin-sheet small-size dipole transducer are determined as length =51mm,width =24mm and thickness =0.75 mm.The selected material is PZT-5A.The structural parameters of the metal substrate are length =59mm,width =32mm,thickness =0.72 mm,the selected material is chromium-nickel alloy,the structural parameters of the fixed skeleton are length =65mm,width=39mm,thickness =3mm,and the selected material is steel.The directivity results of the piezoelectric transducer assembly in infinite waters show that it can work well as a dipole sound source;the test results of the conductivity characteristics of the impedance analyzer show that the transducer assembly is changed in four directions.The substrate of the energy converter has good consistency and corresponds to the simulation results.The fundamental frequency of the X-directional transducer of the transducer assembly mounted on the skeleton is higher than that of the Y-directional transducer,and the transducer is in silicone oil.The resonant frequency corresponding to the peak of the conductance characteristic curve is obviously lower than that in the air,and the frequency band of the conductance curve is wider than that in the air.The sound pressure response level test results in the anechoic pool show that the dipole transducer has three low-frequency resonance peaks,the corresponding frequencies are 1.5k Hz,2.5k Hz and 4k Hz,and the horizontal azimuth directivity results corresponding to each resonance frequency are good,indicating the installation The dipole transducer assembly can effectively identify different orientations of the formation,and can use different operating frequencies to achieve different detection targets.The purpose of this research is to design a small-sized transducer applied to dipole shear wave exploration in the case of small boreholes through simulation and simulation,and to conduct experimental tests on the processed and installed physical objects.It is the research and development of a small borehole acoustic dipole logging tool The basic research has a certain guiding significance...