Analysis on active power transmission characteristics of telemetry drill string in laboratory

The telemetry drill string consists of multiple wired drill pipes connected in series. The transmission rate of telemetry drill string is much higher than that of other MWD signal transmission systems. However, telemetry drill string requires the installation of repeaters after every few hundred meters to compensate the signal attenuation, which leads to an increase in the cost of the system. Therefore, it is of great significance to find out the key parameters that affect the transmission characteristics of telemetry drill string channel active power, and optimize them to reduce the loss of signal power along the telemetry drill string. This work establishes a mathematical model of active power transmission characteristics of telemetry drilling string channel based on circuit analysis and analyzes the influence of each circuit parameter of wired drill pipe on the channel power transmission characteristics by using the numerical analysis method, circuit simulation method and experiment. The results show that the circuit simulations and experimental results are consistent with the theoretical calculations, which verifies the correctness of the proposed mathematical model. With an increase in the number of sections of the drill pipes, the channel power attenuation also increases. Improving the coils inductance and coil coupling coefficient, reducing the eddy current loss, and adopting the coaxial cable with a 75-Omega characteristic impedance reduces the channel power attenuation significantly. This paper provides a theoretical guidance for relay distance improvement, carrier frequency design, and extended downhole battery life improvement.