Method and system for skin effect correction in a multiple transmit frequency induction logging system

摘要

An induction logging tool is disclosed for utilization in conjunction with surface electronic equipment for measuring a characteristic of subsurface formations. A transmit signal which is comprised of a repetitive sequential series of at least three transmit frequencies is generated by coupling an oscillator 30 to a transmitter coil 38 and a plurality of selectable tuning capacitors 32,34,36. A signal characteristic of the response of the formation to this transmit signal is detected at a receiver coil array 52,54 and two phase sensitive detectors 72,74 are then utilized to generate output signals indicative of the magnitude of the quadrature (X) and in phase (R) components of the formation signal. The output signal of each phase sensitive detector is then utilized to accurately determine the X and R component of the receiver coil signal for each frequency by nulling the output of the phase sensitive detector utilizing a closed loop conversion circuit which eliminates errors due to phase and gain variations. The X and R signals from two or more frequencies are then utilized to correct for skin effect in both magnitude and spatial response.