Wide-band Acoustic Source Excitation Technology And Experimental Research

In both cable logging and drilling logging,the improvement of acoustic transducer structure and excitation mode promotes the development and significant evolution of acoustic logging technology,with the increasing difficulty of oil and gas development,logging-while drilling(LWD)occupies a place in the logging market with its real-time and accurate advantages,especially in offshore exploration.Transmitting transducer is one of the key parts of acoustic logging instrument,the intensity of excitation energy and working bandwidth directly determine the quality of logging signal.Strata in different regions have different natural frequencies.When the excitation frequency of sound source is close to the natural frequency of strata and the radiated sound wave energy is strong enough,rich stratigraphic signals will be measured.At the same time,the introduction of wideband inverter excitation technology is expected to realize the reusability of excitation converter or excitation circuit in monopole,dipole and other excitation modes,so as to simplify the excitation circuit and multipole logging instrument.The acoustic logging tool for evaluating the azimuthal anisotropy is mainly the orthogonal dipole acoustic logging tool.While in the field of medical ultrasound and underwater acoustic engineering,wideband transducer excitation technology has achieved initial success,but the equipment is not restricted by space design is more flexible,and more near the transducer frequency broadband incentive study,and in the field of acoustic logging instrument limited space for broadband excitation frequency,power and circuit structure is more strict,therefore,high power,broadband source excitation technology is the technical difficulties of the current in the field of broadband technology research is of great significance.Based on this,the broadband excitation technology of the acoustic logging piezoelectric transducer was studied in this paper.At first,the excitation circuit of sinusoidal sound source was designed.Then,impedance matching network is designed in ADS radio frequency simulation software and parameter optimization is carried out in combination with the equivalent circuit of the transducer.The resulting impedance matching network is combined with the transformer design and modeled and simulated in Maxwell finite element analysis software.According to the Voigt-Reuss model theory of equivalent medium theory,the influence of rock and cement acoustic parameters on the production of model well and the percentage of their volume percentage on the anisotropy of experimental model well are calculated.The finite difference numerical simulation method is applied to simulate the theoretical calculation results.According to the conclusions obtained,the design idea of azimuthal anisotropy model well in laboratory is put forward.According to the design idea,a small size experimental model well is made,and the orthogonal dipole acoustic measurement of the model well is carried out to verify the feasibility and feasibility of the proposed design idea.At last,the whole sound source excitation system is simulated and tested.Simulation and experimental results show that the research and development of broadband source excitation transducer technology,able to work band broadening the 3.5 times,active power 15 d B,a sharp rise in the transmitting transducer excitation bandwidth and incentive efficiency,improve the adaptability of well logging instrument,detecting depth and resolution for subsequent optimization of acoustic logging instrument provides the help.