Downhole pipe selection and arrangement for acoustic drillstring telemetry

Abstract

Drillstring acoustic telemetry is an effective transmission method to retrieve downhole data. In this paper, finite-difference algorithm is used for acoustic wave propagation prediction along the drillstring. An impulse excitation signal of time duration 30.87 µs is transmitted from the downhole and the wave displacement at the receiver is found using finite-difference algorithm. The resultant impulse and frequency responses are plotted and compared for different segments. It is found that the selection and arrangement of downhole pipes plays a vital role in improving the transmission efficiency of extensional waves transmitted through the drillstring for acoustic telemetry, particularly in the high-frequency bands. In order to find the optimal pipe arrangement order, 4 segments of drillstring with lengths d 11 to d 14 (in increasing length between 9.3434 m and 9.8185 m) are arranged in all 24possible permutations. The energy of the frequency response is found for each of the six pass bands for the twenty four arrangements. It is concluded from the findings that placing the shortest pipe at the downhole first, followed by the longest pipe, then the next longest pipe and so on, produces the best possible telemetry performance in terms of optimal acoustic energy transfer.