Simulation and Analysis of Time-Harmonic Electromagnetic Field Through Metal Casing

In this paper, we present a stable analytical method to simulate the electromagnetic (EM) field through the casing. The expression of the EM field consists of the modified Bessel and Hankel functions that avoid the overflow problem in numerical integration. The numerical filter coefficient method of the fast cosine transform is adopted for the integral, which effectively improves the calculation speed on the premise of ensuring the calculation accuracy. As the foundation of the transient electromagnetic (TEM) logging method, we analyse the casing effect on the EM field with various transmitting frequencies. Numerical results show that the EM field over MHz will significantly decay through the casing.