Application of a New Combination Algorithm in ELF-EM Processing

Abstract

With regards to the electromagnetic measurement while drilling (EM-MWD), the extremely-low frequency electromagnetic wave signal (ELF-EM) below 20 Hz is usually used as the carrier of downhole measurement data due to the transmission characteristics of the electromagnetic wave (EM). However, influenced by the low frequency noise of drilling, the ELF-EM signal will be inevitably interfered by field noise, which ultimately impedes decoding. The Fourier band-pass filter can effectively remove out-of-band noise but is incapable of handling in-band noise. Therefore, based on the traditional method, a hybrid algorithm of adaptive Wiener algorithm and correlation detection (AWCD) is designed, so as to enhance the in-band noise processing capability, and the effectiveness of such algorithm is well verified through coding and decoding simulation as well as experimental data. The proposed algorithm, as indicated by theoretical analysis and test data, can effectively solve actual engineering issues, providing methodological references to engineers and technicians.

Investigations on Field Distribution along the Earth’s Surface of a Submerged Line Current Source Working at Extremely Low Frequency Band

“…In 2018, the seabed environment is treated as a three-layered media and the field distribution is numerically investigated [14]. At the same time, the ELF EM signal has widely used in drilling system to carry downhole measurement data where the studies of channel models and demodulation techniques are essential [15]. Meanwhile, the existence of Zenneck surface wave has drawn researchers' attention, which was proposed by Baño [3].…”