Research Of Key Technologies For Deep Geological Exploration Long-Cable Telemetry System

With the improvement of the development of shallow surface resources,the probability of discovering minerals,oil and gas,rare earth and other important resources in traditional exploration space is getting smaller and smaller.The exploration and development of deep earth resources will be an inevitable choice to ensure national resource reserves.With the advancement of domestic deep resource exploration technology,the data detected by exploration instruments for deeper strata and more complex geological structures has higher dimensions,more parameters,and larger data volumes.The long-cable telemetry system in deep explorationan is an important part of the data communication between the ground and the underground.But the research on telemetry system in our nation begins late,and there is a major gap compared with the products of Schlumberger,Halliburton and other companies abroad.Therefore,researching various key technologies of telemetry system to meet the increasingly high demand for data remote transmission has become an urgent work.In addition,the research on the key technologies of the long-distance cable telemetry system for deep exploration can also be applied to environmental geophysics,nuclear logging and other occasions that require long cables to achieve high-speed data transmission in addition to the field of deep resource exploration.Long-distance cables have few available spectrum resources and severe highfrequency attenuation,which is not conducive to high-speed signal transmission.In order to design a telemetry system that can make full use of the channel bandwidth,it is first necessary to understand the basic characteristics of cables in deep exploration applications through modeling and simulation,which is also the basis for subsequent research.After that,appropriate coding and modulation techniques can be adopted according to the channel characteristics to maximize the utilization of the channel bandwidth and reduce the system bit error rate.In addition,in order to reduce the impact of high-frequency attenuation of long cables on communication,how to compensate for high-frequency signals is also one of the keys to improving the transmission performance of the telemetry system.Finally,the synchronization performance of the telemetry system will directly affect the decoding accuracy of the receiver.Therefore,the highly reliable synchronization technology is also the research goal of this paper.First of all,this paper establishes the distributed parameter model of the seven-core armored logging cable through the transmission line theory,and uses the finite element method to model the seven-core armored logging cable and calculate distributed parameters such as distributed capacitance,distributed resistance,distributed inductance,and distributed conductance.The influence of the underground high temperature environment on the distribution parameters and transmission characteristics is discussed,and then the insertion loss of the 7,000 seven-core armored cable under various working modes is analyzed,which guides the design of various parameters of the cable telemetry system.In terms of coding and modulation technology,this paper studies and discusses the advantages and disadvantages of Manchester coding,PAM4,and DMT when these modulation and demodulation technologies are applied to long cable transmission.In order to ensure the reliability of the telemetry system,the performance and complexity of various error detection and error correction codes such as CRC,BCH,and RS are compared.Based on the actual needs of deep exploration applications,DMT is selected as the modulation method of the cable teletransmission system,and the RS code is used as the error correction code.In terms of channel equalization technology,this paper firstly studies the relationship between time-domain equalization and frequency-domain equalization and their respective characteristics.In the time domain,a combination of pre-emphasis and equalization is used to balance the output power of the transmitter and the signal-to-noise ratio of the receiver.According to the armored cable’s characteristics in the frequency domain,the block training sequence is used to realize the channel estimation,and the hardware logic design scheme of each equalization module is given.In the aspect of signal synchronization technology,this paper expounds the realization method of symbol synchronization and sampling clock frequency synchronization,tests the performance of synchronization sequences such as Zadoff-Chu sequence,m sequence,etc.,and proposes a synchronization sequence design method based on FFT oversampling.According to the characteristics of the hardware circuit,the corresponding resource optimization scheme of the signal synchronization logic is studied,and the simulation is carried out to verify the feasibility of the optimization scheme.Finally,this paper designs and implements a long-cable telemetry system.After testing,the telemetry system can reach the highest transmission rate of 1.4 Mbps on 7000 meters of seven-core armored cable,and the bit error rate is better than 10-8.The system parameters can be adaptively adjusted according to the transmission characteristics of the cable,so as to achieve a communication rate of more than 900 kbps on a sevencore armored cable up to 11,000 meters long.The telemetry system achieved the design goal,and successfully passed the acceptance of national key research and development program of china.