| Petroleum is a strategic resource,and well logging is an effective means to detect petroleum.Transient electromagnetic logging is a new logging method developed on the basis of induction logging.It borrows ideas from geophysical exploration and has the advantages of wide transmitting signal band,rich information and covering one frequency band at a time.To detect the remaining oil,the formation conductivity curve under cased-well condition is required.Transient electromagnetic logging response waveform under casing well contains formation conductivity information,from which formation conductivity can be obtained.In this paper,the theory of electromagnetic field and the related calculation formula based on transient electromagnetic logging are introduced firstly.The electromagnetic fields of plane waves in three layers of conductive media and potential function of twolayer medium on cylindrical interface are derived.Fourier transform is used to calculate the frequency spectrum's formula of transient electromagnetic logging response.With the help of Doll geometric factor,the geometric factor theory of transient electromagnetic logging and the useful signal calculation formula of transient electromagnetic logging are given.A stepper motor control system and a transient electromagnetic experiment system of one transmitting coil and receiving coils are established.The transient electromagnetic response waveform of open-well and cased-well is measured.The data collected are processed and the logging curves with different vertical characteristics are obtained.It shows the response characteristics of logging curve to horizontal aluminum plateThe actual measured waveform of 5.5 " cased-well is processed.The geometric factors of the casing well are obtained by the response of the collar of the cased-well.The formation conductivity curve under cased-well condition is obtained by deconvolution with differential geometric factor and original logging curve and it is compared with the formation conductivity logging of open-well.There is consistency and difference between the two curves.The characteristics of conductivity curve through cased-well are analyzed,and the oil layer and the flooded layer are distinguished.The feasibility of transient electromagnetic logging in cased-well is discussed.Finally,according to the waveform shape after subtracting the response waveform at different depth,the correction idea of formation conductivity curve of casing well is proposed.The prospect of the correction work is given. |
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