Research On Acoustic-Electric Combined Transient Electromagnetic Well Logging Method

When the piezoelectric crystal used in acoustic logging is motivated by high voltage, a transient electromagnetic field will be generated. This transient electromagnetic field propagates in the well and its response carries the message of formation conductivity. This transient electromagnetic field response used to be regard as interference signal, while the message of formation conductivity it carries is studied in this paper. First, after analysing the transient response waveform of piezoelectric transducer, two kinds of exciting wave is chosen: jump function and Gaussian function. Second, computational formula of transient response of piezoelectric tube in open hole, real axis integration method, is derived in detail. And relevant algorithm is implemented, two kinds of response waves is gained. Last, the waveform of Ez, H and Er is analysed. It can be found that the amplitude of Ez varies considerably while the formation conductivity varies. So the formation conductivity can be read off from the amplitude of Ez. The maximum value of Ez is nearly linear with formation conductivity under the condition of short spacing and different formation conductivity. The maximum value of difference of Ez is nearly linear with the difference of formation conductivity under the same condition. The relationship changes when the spacing gets lager. Formation conductivity can be gained directly from Ez.Excitation system of array acoustic well logging, depth acquisition system as well as measurement system of signal acquisition and A/D conversion have been designed.The functions of filtering, magnification, A/D convertion, data transmission, data processing, data storage and real-time display of wave form are achieved by measurement system. Millivolt siginal can be sampled correctly. Depth acquisition system reads the message of depth successfully. Excitation system realises its function by controlling FET IFR460. Theoretical and experimental basis is providesd to further studying of acoustic-electric combined well logging instrument.