Research on Impedance Model of Intelligent Drill String Based on the Average Transformation Theory

Cable transmission has its intrinsic advantages and it is the development tendency of intelligent drilling among all kinds of signal transmission. According to the structure characteristics of the intelligent drill string, this paper analyzes the transmission line distribution parameters of intelligent drill string combined with average transmission theory; transfer matrixes of single drill pipe, drill pipe joint and that of cascaded transmission line between them are all calculated by the transmission line transfer function; impedance model of intelligent drill string communication channel model are built according to that transfer matrix based on the two-port network, then this model is simulated by experiment and the result is analyzed; curve of error rate is got and the influence of different signal-noise ratio, different transmission rate and different transmission distance on signal transmission performance are analyzed. This model simplifies the calculation, and the frequency characteristics and attenuation characteristics of transmission line are obtained under the analog signal and the digital signal, then the average transmission signal characteristics of intelligent drill string is analyzed by intuitive squiggle. Maybe this paper could provide some theoretical guidance for intelligent drill string.