Optimization of acoustic communication for industrial drilling

Abstract

Drill string acoustic telemetry is an effective transmission method to retrieve downhole data in drilling applications. In practice, pipes used for drilling deep wells have slight variation in length. The arrangement of downhole pipes plays a vital role for improving the transmission efficiency of extensional waves transmitted through the drill string. Finite-difference modeling produce the comb-filter-like channel response (patterns of pass bands and stop bands) due to the presence of coupling joints in the metallic drill string. In this paper, channel response of the 3rd to 6th pass bands for 4 different pipe arrangements, namely, ascend-only, descend-then-ascend, ascendthen-descend and descend-only, are compared for finding the optimal pipe arrangement. Drill pipes and joints with dimensions scaled down to (1/24.2)th of the actual drill string dimensions are used to set up an experimental measurement system for 8 pipes. Channel response measurements are taken from the experimental setup by arranging the 8 pipes in the orders mentioned above. It is concluded from the findings that the ascend-then-descend pipe arrangement produces the best possible telemetry performance in terms of maximum acoustic energy transfer.