Study On The Transmission Technology Of Communication While Drilling System

With the development of drilling technology, more and more undergroundinformation need to know, but the available transmission system using cable can notaccomplish the goal of measurement while drilling (MWD). Therefore, electromagneticmeasurement while drilling (EM-MWD) system, as a noval technology, attracts more andmore attention in the drilling industry. The transmission technology of the EM-MWDstytem is the core of the MWD system, and it is important to design a good transmissiontechnology used in the underground environment.This paper analyzes the main affects that have impact on electromagnetic signaltransmission, and makes a further study of the EM-MWD signal transmission byanalyzing the equivalent electromagnetic signal transmission model. On the basis of themodel, the simunation is done to analyze the relationship between the received signalstrength and the depth of drilling equipment. The simulation shows that the receivedsignal strength decreases sharply in the beginning of running the drilling tool into the well,but the strength will be stable after the depth reaches to some extent. The simmunationresult will offer the reference to the design of system and analysis of the on-site test.In the process of measurement while drilling, the signal is mixed with the noisecaused by the equipment on the ground and affected by the underground channel.Therefore, proper channel code and modulation technology are needed to achieve the goodperformance. In order to improve the performance of the system, we have compared themodulation methods of BPSK and MSK, and the channel codes of hamming code andcycil code. Finally, we choose cycil code and BPSK modulation in the EM-MWD system.The hardware platform of the system based on MCU is introduced, and the designand implement of the EM-MWD system is discussed. In the on-site test, we use theelectromagnetic signal transmission model to explain the phenomenon of the signalstrength variation, and evaluate the signal transmission technology.