A Theory Analysis and Experimental Study on Acoustic Transmission Properties in Drill String

In order to validate the acoustic transmission properties in drill string,and get the right frequency point or band for underground information transmission,using Φ127.0 mm drill pipe as the research object,and analyzed the relationship between frequency and wave number of drill pipes with different lengths based on the frequency equation of ideal drill string.The analysis results show that unevenness of drill pipe length will lead to smaller intersection of drill string pass band; if each cycle of drill string consists of drill pipes with different lengths,the pass band will become narrow,or,in some frequency bands form very wide stop band because of no overlap.Based on transient response equation of ideal drill string,the reflection action of drill pipe connector to acoustic wave has been analyzed,to get transient properties of acoustic wave through a lot of drill pipes.Through indoor experiments on acoustic transmission properties with the full size joint,1.5 m-long drill pipe,we studied the transmission properties of different-frequency acoustic waves in different-length drill strings,verified that comb filter and dispersion phenomenon exist in the acoustic transmission in drill string,and got some frequency scope or frequency band that was suitable for acoustic transmission in drill string.