Communication Technology Study On Short Distance Acoustic Transmission Characteristics In Drill String

Rotary steerable drilling tools system is the core component of rotary steerable drilling system. The data can be transmitted to Measure While Drilling(MWD) unit from various sensors in the near-bit electronic storehouse through a short distance communication component and then transmitted to the instrument on ground by MWD unit. And it delivers the corresponding data to MWD system, and then sends data to the ground station. So the system needs a high speed, accurate and reliable wireless communication technology to send data from the rotation stable platform to the relatively static MWD,This paper mainly studies the acoustic technology to solve the problem of information propagation in short distance. It analyses the basic theory of acoustic wave, the propagation characteristics of abrupt change in the cross sectional area of a pipe and intermediate intubation.To study acoustic wave propagation characteristics in short distance drill string, the experiment system of acoustic wave propagation of short distance was established in a 1,28 m drill string. The square-wave voltage as a driving signal was used in the experiment. The directions of exciting drill string included axial excitation and radial excitation. The exciting frequency ranged from 4Hz to 60 Hz. The sensors located in different place on the receiving ends. The experiments research the acoustic wave’s signal sensitivity parameters to the driving voltage, exciting frequency, exciting orientation and sensors direction.The test results show that acoustic wave signal would attenuate in the process of propagation. There also contained echo and large number of noise in acoustic wave. The driving voltage should be as stronger as possible in the range of energy consumption allowed in the downhole tools. The radial force excitation is the best way to excitation. The best measuring position of sensor is radial investigate.