Research On The Signal Coding And Data Fusion Method Of EM-MWD In Underground Coal Mine

With the development of drilling technology,special drilling techniques such as directional wells and highly deviated wells have become more important.Measurement while drilling technology is wildly used in the field of oil and gas drilling.In recent years,it has also been extended to the field of coal mine safety,and has played an increasingly important role in coal mines and underground coalbed methane construction.During the drilling process of special drilling,the key to ensuring the quality of drilling is to quickly,effectively and accurately control the well trajectory for timely correction.The application of the technology of transmitting real-time data from the sensor at the drill bit to the surface in MWD can minimize downtime and improve work efficiency.The research on measurement while drilling system in underground coal mines is still in its infancy in our country,and there are deficiencies in technology and equipment,especially for the special construction conditions underground in coal mines.The complex operating environment and hidden safety hazards lead to many advanced technologies and equipment on the ground cannot be used directly.Therefore,it is necessary to develop technology and equipment suitable for underground production conditions in coal mines on the basis of digesting and absorbing advanced technologies on the ground.Based on this theme,this thesis studies the attenuation characteristics of the electromagnetic signal transmission of the underground electromagnetic wave while drilling instrument for the special situation of underground coal mine production,and provides a theoretical reference for equipment design.On this basis,this thesis studies the channel coding technology and multi-channel data fusion method of underground electromagnetic wave measurement while drilling in coal mines to reduce the bit error rate in the working process of the system and improve the reliability and transmission depth of the system.Based on this,a measuring instrument for electromagnetic waves while drilling underground in coal mines has been developed.The main research work and results achieved in this thesis are as follows:1.Analyzing the technologies and theories involved in the underground electromagnetic wave measurement while drilling system in coal mines,including the composition principle and structural block diagram of the EM-MWD system,signal excitation method and electromagnetic wave attenuation characteristics in the formation.The system uses asymmetric dipoles as transmitting antennas.Based on the basic principles of electromagnetic waves,with the help of equivalent transmission line method,the attenuation characteristics of electromagnetic signal transmission of underground electromagnetic wave MWD instruments in coal mines are studied,and factors such as formation resistivity,drill pipe resistivity,emission frequency,and lower drill pipe length are analyzed.The results show that increasing the length of the drill string below the insulation pip and reducing the frequency of the transmitted signal are beneficial to reduce signal attenuation,and the increase of formation resistivity is beneficial to signal transmission.2.Aiming at the three channel codes of BCH code,trellis code modulation and Turbo code,combined with the characteristics of the communication channel and transmission data format of underground electromagnetic wave measurement while drilling in coal mines,through theoretical calculation and simulation,the error performance of the three channel codes is systematically analyzed.The coding method suitable for the communication channel of electromagnetic wave measurement while drilling in coal mine is obtained.3.The multi-channel data fusion method is studied,and the single-channel data is processed by Kalman filter,combined with simple convex track fusion algorithm,cross-covariance track fusion algorithm and layered track fusion algorithm for analysis and calculation,and the three are verified by simulation.The feasibility of this kind of track fusion algorithm is compared,and a track fusion algorithm suitable for underground electromagnetic wave measurement while drilling system in coal mine is obtained.4.The prototype composition and working mode of the underground electromagnetic wave measurement while drilling instrument in coal mines are introduced,and the design of the in-hole instrument and the orifice instrument is given.Conducted a variety of prototype work experiments,tested the bit error rate under different methods by changing the size of the receiving current,tested the signal processing ability of the orifice instrument,completed the ground transmission experiment,the ground transmission experiment with the pump,and the underground transmission experiment.At the end of the thesis,the main contents and results of the research are summarized and the future research work is prospected,which will provide a certain reference for subsequent research.