Relationship Between Detection Depth and Transmitting Frequency of Transient Electromagnetic Logging Instrument

Abstract

Transient electromagnetic technology is used in production wells for logging exploration, the detection depth of instrument is affected by the frequency of transmitting bipolar rectangular wave signal. When the signal is transmitted, the steady primary magnetic field with closed magnetic circuit is established in the media around well, and the distribution of the magnetic force line is related to the transmitting frequency. The increase of the density of magnetic force line in the formation causes the increase of the detection depth of the instrument. Therefore, it is necessary to set appropriate transmitting frequency to detect electrical characteristics of media around well accurately and effectively. In the experimental environment of single-tube string, the decrease of the transmitting frequency (the increase of the transmitting pulse width) increases the logging detection depth, the amplitude and attenuation time of the receiving waveform. The effects of transmitting frequency of rectangular wave on receiving wave form reveal that the magnetic resistances of media around well affect the density of magnetic force lines, and reach a conclusion that decease of the transmitting frequency increases the density of magnetic force line in casing and formation around the well to effectively increase the detection depth of instrument. These investigations are helpful to determine the optimal configuration and to set an appropriate value of transmitting frequency in order to further much more accurately detect the electrical parameters of the detected target formation.