Abstract
A telemetry drill string system consists of a string of wired drill pipes, and high-frequency signals pass the adjacent drill pipes through inductive couplers. Such a system is used to upload downhole information at high data transmission rates for measurements while drilling (MWD). Since the signal energy attenuates greatly in the system, many repeaters must be provided to ensure signal transmission. A reduction in the signal transmission in a telemetry drill string can extend the relay distance and improve the reliability of the transmission system. In this study, the transmission characteristic of the rod of the wired drill pipe is studied using transmission line theory, and the transmission characteristic of the inductive coupler is studied using high-frequency circuit theory. Using impedance matching between the transmission line of the rod and the inductive coupler, external impedance compensation elements, including a capacitor and a resistor, are recommended, and the electromagnetic parameters of the wired drill pipe are determined. Based on the determined electromagnetic parameters, certain changes in the external impedance compensation capacitance and resistance can lead to impedance mismatch between the transmission line and the inductive coupler. This will generate a reflected signal at the transmission line, and the vector superposes with the transmitted signal. The terminal reflection coefficient of the transmission line is controlled by increasing the compensation resistance value to enhance the signal amplitude, which can compensate the transmission loss when passing through the inductive coupler to a certain extent. Thus, the signal transmission capability of the telemetry drill string can be improved, allowing for long-distance signal transmission or drastically extending the relay distance, while maintaining a certain channel bandwidth.
Highlights
Measurement while drilling (MWD) is a modern drilling assistant technology for real-time downhole information measurement and transmission during the drilling process
Because the voltage transmission coefficient of the inductive coupler has a great influence on the transmission characteristics of the channel, current methods focus on reducing the signal energy loss of the inductive coupler to increase its voltage transmission coefficient in order to improve the signal transmission capability of the telemetry drill string
Based on transmission line theory and circuit theory, this paper studies this problem and proposes a method to improve the channel transmission characteristics using an impedance matching analysis between the coaxial cable and inductive couplers
Summary
Measurement while drilling (MWD) is a modern drilling assistant technology for real-time downhole information measurement and transmission during the drilling process. Mathematical Problems in Engineering a drill pipe to transmit high-frequency electromagnetic signals, and its data transmission rate can reach 2 Mbit/s at a 2 MHz channel bandwidth (using quadrature phase-shift keying modulation or QPSK modulation). In this system, the signal transmission requires a large number of repeaters, and the relay distance is the length of 30 drill pipes in a series. Because the voltage transmission coefficient of the inductive coupler has a great influence on the transmission characteristics of the channel, current methods focus on reducing the signal energy loss of the inductive coupler to increase its voltage transmission coefficient in order to improve the signal transmission capability of the telemetry drill string. Based on transmission line theory and circuit theory, this paper studies this problem and proposes a method to improve the channel transmission characteristics using an impedance matching analysis between the coaxial cable and inductive couplers
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