Using the Superposition Principle and Edge Current Model to Compute Impedance of the Coil in a Logging Tool

T. Zhao, G. Minerbo, J. Hunka, and G. Hazen
Schlumberger
Sugar Land, TX

Coil antenna is the simplest form in well-logging tools for resistivity measurement of the formation. This paper introduces how to accurately compute the impedance of the coil with very thin wires at high frequency, and with the complex borehole structure, e.g., metal housing and collar.

A 3D RF electromagnetic wave in frequency domain is used. An alternate array of transmitters and receivers in the same coil is modeled to obtain the mutual impedance instead of self impedance. A trapezoidal weight is applied to both transmitters and receivers. A superposition method is applied to include the effect of the wire thickness. It is observed that the COMSOL amplitude matches the measured results very well.

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