The Research Of Near-bit MWD Data Transmission System

Wireless communication technology has been used more and more frequently with the development of science and technology.However,in some special areas like petroleum drilling and geological drilling,the normal wireless communication technology can’t meet the demand because the signal is absorbed too much by its special medium,so new transmitting method should be designed to solve the problem.In the normal measurement-while-drilling system,the sensor is set above the power drill and at least 15 meters far from the drill,so the data got is actually not real.To get the original data which near the drill,a wireless communication link is requested to establish so as to set the sensor near the drill,which is the difficult and hot spots in measurement-while-drilling area(MWD),called short-range communication of near-bit.In the normal measurement-while-drilling system,the data can be transmitted by mud pulse,electromagnetic wave and acoustic wave.However,the data rates of these transmissions can’t meet the need.In this paper,a near-drill wireless communication system with magnetic induction coupling is studied by combining the feature of near-drill data whose transmission distance is short and referring the high speed intelligent drill pipe developed by IntelliServ company.First of all,through theoretical analysis,the circuit model of near-drill wireless communication system is established by referring the principle of electromagnetic induction and the transformer circuit model.Secondly,this transmission method is proved to be feasible by simulation experiments in the ground,at the same time,the characteristic curves of transmission channel is obtained to provide basis for the design of magnetic coupling coil parameters and the choice of frequency.Last but not least,in the basis of combining underground working conditions and the exist modulation and demodulation methods,the modulation circuit based on AD9832 and demodulation circuit based on NE564 is designed and successfully transmitted data the experimental environment.