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 to a transmitter coil and a plurality of selectable tuning capacitors. A signal characteristic of the response of the formation to this transmit signal is detected at a receiver coil array and t wo phase sensitive detectors are then utilized to generate output signals indicative of the magnitude of the X and R components of the formation signal which is in phase with a reference phase signal. The output signal of each phase sensitive detector is then utilized to accurately determine th e 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 conversio n 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.