Research On MWD Electromagnetic Signal Transmission Characteristics Based On Electrictelemetry Drill String Transmission

The information transmission rate of MWD signal transmission method widespread used athome and abroad currently is relatively low, and could only simplex communication. Thetransmission speed of telemetry Drill Pipe system has been successfully reached2Mbit/s,while mud pulse transmission technology currently used by only8~10bit/s. Theelectromagnetic transmission technology can provide a higher transmission speed of100bit/s,but will be limited by the depth and the formation resistivity.Telemetry Drill Pipe transmission system studied in this paper is a novel downholetelemetry systems, with dual function of a regular drill pipe and also a two-way high-speedsignal transmission link. Theoretical research and simulation analysis on its transmissioncharacteristics has great significance of engineering applications, and MWD technology willbe upgraded to a new level.Telemetry drill string system uses the principle of electromagnetic induction to realize thetransmission of data to adjacent pipe join through a Non-contact line coupling device whichcomprises a conductive coil installed in the contact surface. When two connections arebrought together, the coil in one end of the first is brought into close proximity with the coilin one end of the second. A carrier signal in the form of an alternating current flowingthrough the coil in either segment produces a changing electromagnetic field that inducescurrent flow in the other coil, thereby transmitting the signal to the second joint. In this paper,based on transmission line theory and the law of electromagnetic induction, establishing themathematical model of the electrical telemetry drill pipe electromagnetic signal transmissioncharacteristics, and progressing numerical analysis on the transmission characteristics of thedrill string through Matlab programming. By seeing telemetry drill pipe as “Road”, and analyzing the signal transmission using classic transmission line theory, the engineeringanalytic functions can be obtained directly, which is intuitive at results and convenient atanalysis. By numerical analysis, factors impacting the transmission characteristics of drillstring can be found, which laid a solid foundation for further optimization of the telemetrysystem.