| In the process of exploration and exploitation of oil and gas wells,it is necessary to obtain relevant data of downhole measuring instruments in real time so that testers can take various countermeasures and adjust operating procedures in time,thereby reducing blindness in drilling work and improving drilling efficiency.As the development of the oilfield enters the later stage,the exploited oil layer is getting thinner and thinner.The sensor,in conventional MWD technology,measuring point that senses temperature,pressure,formation information and other data is as long as 8m to20 m from the bottom hole bit.When the bottom hole drill bit crosses the formation boundary,the data sensed by the sensor is relatively lagging,and the changes in the formation boundary cannot be sensed in time,making the attitude adjustment of the drilling tool not timely,causing a large amount of loss of oil and gas reservoirs,and in severe cases,geo-steering may be in trouble.In order to solve the problem caused by the lag of data information,it is urgent to develop a wireless short transmission system for near-bit measurement to realize the real-time transmission of near-boring sensor data information.This article mainly studies the key technology of magnetic coupling wireless short transmission measurement near the drill bit.First,the transmission mechanism of the magnetic coupling short transmission system is analyzed,and the equivalent model of the transmission system circuit is proposed.The transmission coil is excited according to Maxwell's equations.The field division is deduced and calculated,and the characteristics of reactive power oscillation in the near-field region of the transmitting coil are obtained,which provides theoretical support for subsequent system design and model simulation.Secondly,a downhole magnetic antenna transmission model was established in the finite element simulation software for computer solution and analysis,and the attenuation law of the magnetic field intensity excited by the coil on the screw under different frequency and different magnetic core factors was studied,and the downhole instrument's performance was studied.The special working environment influences the distribution of magnetic field lines.Improvement measures to enhance the magnetic field strength such as bilateral resonance compensation and slit treatment of the protective cover are proposed to enhance the transmission performance of the system.Finally,according to the magnetic field attenuation law and the structure of the downhole instrument,the parameters of the transmitting coil are calculated and modified,the impedance characteristics of different bilateral resonance compensation circuits are analyzed,and the optimized SS resonance compensation structure is selected.And studied the 2FSK signal modulation and demodulation scheme which is easy for system transmission,designed and developed a simple and reliable structure,good sealing,high applicability,magnetic coupling wireless short transmission system for near-bit measurement.The key technology of near-bit measurement wireless short transmission can provide accurate and reliable scientific decision-making basis for drilling operation site construction in real time,improve drilling tool trajectory control accuracy,reduce drilling costs,and meet the needs of oilfields to increase reserves and production and improve economic benefits,which can improve The technical level of my country's directional well technology and its competitiveness in the international drilling technology service market. |
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