| Oil is indispensable energy in today’s world.Therefore, Therefore, the exploration of oil and the transmission of information during the drilling process have become a hot research topic.However, the real-time transmission of logging data has become a bottleneck of logging study. Now matured and applicated transmission technology are cable transmission and mud pulse transmission. But cable transmission costs too high, and operates troublesomely. Mud pulse transmission rate is slow and cannot be used in underbalanced wells and gas wells. In view of the shortcomings of the above two methods, this paper studies the electromagnetic wave transmission technology of electromagnetic measurement while drilling. This paper’s main contents is as follows:Firstly, this paper introduces the basic principle of electromagnetic wave transmission of electromagnetic measurement while drilling, and comparative analysis the the advantages and disadvantages of several electromagnetic signal of incentives. This paper also studied the influence factor of the distance of the electromagnetic wave signal in formation transmission, and the simulation was carried out. At the same time, the paper analysis the equivalent model of electromagnetic wave transmission of electromagnetic measurement while drilling, and the relationship simulation diagram between the ground detection voltage and the metal ring, the upper length of insulation section and the transmission depth is given.Secondly, baseing on the electromagnetic transmission properties of the formation, the paper selectd VLF as the signal transmission frequency. According to this frequency, this thesis studied the spectrum characteristics and bit error rate of several modulation schemes that it being used extensively now. Then, the minimum frequency shift keying(GMSK) of Gauss filter used in this paper is analyzed from the following aspects: the principle, the encoding and decoding scheme and the performance analysis. After the channel coding, Hamming codes, cyclic codes and convolutional codes is studied, which focuses on the convolutional code principle, decoding algorithm and performance analysis.Finally, duing to electromagnetic signals along the formation propagation attenuation intensely, interference strongly, the useful signal is almost buried in noise interference, so the paper used 50 Hz notch filter and a low pass filter to remove interference noise and extract the useful signal,then put it into zoom, demodulation circuit to obtain the useful logging information in order to adjust downhole equipment work. |
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