Signal wireless transmission behaviors along the drillstring using extensional stress waves

Real-time data collection about the drilling process is an effective way of improving the drilling efficiency. Drillstring acoustic telemetry is an alternative wireless transmission method to retrieve downhole data. A time-domain algorithm based on finite element method is proposed for acoustic wave propagation along the drillstring immersed in viscous drilling fluid. The effects of the channel boundaries, transceiver positions and modulation modes on acoustic transmission behaviors are analyzed. Then, the narrow pulse on-off keyed modulated signal transmission experiments are performed by applying the longitudinal excitation to the length-limited simulated drillstring in the axial direction of pipes. The results show that the acoustic signal transmission rate is 77 bit/s along a 6.2-meter simulated drillstring under the excitation power of 1W in the laboratory.