The Key Technology Research Of NMR Logging-while-drilling

LWD NMR logging is a new topic of domestic NMR logging，compared withcable NMR logging, which has a clear technological advantage, but there are alsotechnical problems need to be resolved, such as the the downhole power system design,downhole data filtering algorithm design, influencing factors of the inversion method andalgorithm design. The paper proposed an underground power system design according tonuclear magnetic resonance logging-while-drilling underground power supply mode, andin accordance with the NMR echo train signal is different from the original echo signalspectrum characteristics proposed using9/7lifting wavelet algorithm echo train signalfiltering. Based on comparative analysis of the influencing factors of the inversionalgorithm to effectively to improve the signal-to-noise ratio of the echo train.Firstly, the paper introduces the basic theory of NMR logging while drilling, theoverall structure of the LWD-NMR tool and the distinction of LWD-NMR loggingcompared to cable NMR logging, and explains the technical problems, then analysesunderground power supply, power supply requirements, and design a power systemwhich includes multiple switching part and the secondary voltage conversion part. Thenanalyses different spectral characteristics of the echo string signal and the original echoof LWD-NMR logging, proposed multi-resolution wavelet algorithm and realized thealgorithm in hardware, Finally, The paper analysed the impact factor of the inversionalgorithm, and filtered echo train signal to obtain the inversion spectrum and porosity.The results show that the power supply system can effectively solve the problems ofNMR logging while drilling in the multi-channel power switch and the voltageconverting, and the wavelet algorithm effectively extract the echo signals in the theoriginal echo train data, suppress noise, SNR increases by about65%, and theexperimental results show that, in the case of parameters to select appropriate and high signal-to-noise ratio, the inversion results and porosity can better reflect the formationproperties.