Detection of the Good Conductor Outside Casing Using Comparative Receiver Coil System

摘要

Electromagnetic signals are transmitted and received by electromagnetic probe,which is an important part of transient electromagnetic logging tool.The detection effect of electromagnetic flaw detection and the extraction ability of the electromagnetic resistivity measurement directly depend on the sensitivity of electromagnetic probe.The two signals outputting from comparative receiver coil are subtracted and amplified,and then a new total outputting signal is formed.When there is an anomalous conducting body around wellbore,the attenuation trend of the total outputting signal has significantly changed,due to the difference of the positions between the two coils and the anomalous body,-to reach the requirement of high sensitivity signal measurement.The electromagnetic probe,which consists of a transmitter coil and a comparative receiver coil system,is designed.The winding mode of the transmitter coil and the receiver coil is overlapped.The probe is placed into steel casing for experimental test.When a good conductor is placed on the outside of casing,the attenuation characteristics of total outputting signal are changed obviously.It is verified that this type of electromagnetic probe can effectively identify the good conductor,which is placed on the outside of casing.The signal sensitivity of comparative receiver coil system is higher compared with the signal sensitivity of the absolute receiver coil system.Therefore,the electromagnetic probe by use of comparative coil system is more adaptable to complex well conditions,which improves the logging resolution and increases the detection depth.In order to detect weak signal in through casing resistivity logging,the performance of instrument using comparative receiver coil system is superior to that of absolute receiver coil system.A new research and development direction for the improvement of the electromagnetic probe of the through casing instrument is provided by the experimental results.