| In modern oil/gas exploration and development industry,there are many new technologys develop for complex wells and non-conventional wells.To make the adjustments of operating process more reliable and make sure the effectiveness and safety of drilling,these new technologys require the appliaction of real-time acquisition and transmission of downhole operating datas and geological parameters.With the increasing demands for the measurements-while-drilling(MWD)technique,the capacity of data transmission should be increased to acquire downhole informations as much as possible.The intelligent drill pipe system has been realized abroad and it adopt non-c ontact signal transmission techniques,which avoids many common problems(wire wear,poor contact,etc)in conventional wire transmission technology.And this data transmission system can realize high transmission rate reach 2Mbps,which is sufficiently higher than present transmission techniques using electromagnetic wave or mud-pulse.It achieves non-contact signal transmission and breaks the technology bottleneck of dat a transmission while drilling.Although the general structure of the intelligent drill pipe has been understood,the magnetic transmission method which is the key part is still not public.Therefore,building the chanel model of magnetic transmission and designing the signal transmission drill pipe are essential for the future application.The purpose of this paper is to study the fundamental theory of this advanced transmission system and perform experimental verifications,which will promote the development of this technology and form the basis for the future application.This paper first analyzes the transmission mechanisms of magnetic coupling coil.The circuit model for magnetic coupler is built based on the matured circuit model for high frequency transformers and improved by the comparison study between numerical results and measured results for real coupler.Then the transmission model of magnetic inductive transmission channel is obtained.To solve the problem of attenuation of the multistage signal transmission,capacitance compensation is adopted to increase the amplitude of the resonant frequency.The frequency characteristic curves of the signal transmission for the whole channel are given and the frequency of magnetic induction transmission is obtained.The sine-like wave technology is studied and adopted in this paper.The sine-like wave is more effective and reliable than traditional ways in terms of carrying signals.The sine-like wave shows great advantages for transmitting information.In this paper,the mechanisms of sine-like wave modulation were deeply studied and this effective technique also is introdued into present magnetic inductive transmission system,which highly improves the communication efficiency.According to the demands for the signal transmission function of drill pipe and joints,new designs of these two parts are made.The mechanical simulation model is built and this model was used to analyze the strengths of the joints and drill pipe.The simulation results demonstrate that the structure and strength can meet the requirements of operations.Besides,structure of the magnetic transmission coupler,magnetic material and coupling coil are also deeply studied and optimized.Using the multi-physics coupling analysis software to simulate the electromagnetic field of the coupler,the magnetic field distribution and signal transmission frequency characteristics are obtained.Based on the principles of Frequency-Shift Keying and Sine-like technology,the circuits of modulation and demodulation are developed,and full size prototype of drill pipe for Signal transmission experiment is manufactured.The the experimental system is established for testing the two different communication model.Based on experimental platform for drilling,the communication in the magnetic induction transmission channel is further verified. |
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