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.
Highlights
Two transmission modes are mostly applied to the measurement while drilling (MWD) process, namely stand pipe for mud pulse detection [1] and electromagnetic (EM) wave transmission [2,3]
It is proven by theoretical studies that the signal strength will gradually decrease as the frequency of the MWD EM wave increases [3]; after taking engineering factors into consideration, extremely-low frequency electromagnetic wave signal (ELF-EM) below 20 Hz is commonly adopted as the carrier
The combination is easy to apply, reliable in filtering, and of universalityofto the ELF-EM processing, which has been proven to be practical in enhancing the signal to noise ratio (SNR) of the received signal and reducing the bit error rate of the MWD communication
Summary
Two transmission modes are mostly applied to the measurement while drilling (MWD) process, namely stand pipe for mud pulse detection [1] and electromagnetic (EM) wave transmission [2,3]. The Fourier transform-based denoising method is suitable for stationary signals, but it has a poor processing effect on non-stationary ELF-EM signals whose frequency changes with time. The key to extend transmission depth and lower decoding error rate is whether the in-band noise of ELF-EM signal can be filtered without affecting signal source. Extend transmission depth and lower decoding error rate is whether the in-band noise of ELF-EM signal can be filtered without affecting signal source. To work out anTherefore, effective method removing the method of removing the in-band noise has become a key to the transmission of EM-MWD.
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