Development Of Downhole Wireless Transmission Short Section

In the Rotary Steerable Drilling System(RSS),the information transmission between the guide head and the Measurement While Drilling(MWD)occupies a crucial position,so the transmission rate and reliability of the information transmission mode are increasingly demanding.The downhole wireless transmission section is used in RSS.In the actual drilling process,various functional sections that separate the drill pipe are installed on it,making the data transmission become a technical difficulty.In order to realize the bidirectional information transmission between the guide head and MWD,the traditional solution is to connect MWD with the guide head via the cable.However,due to the high-speed rotation of the measuring and transmitting motor in the drilling process and the corrosion of the drilling fluid,the cable is easy to be damaged,the signal cannot be transmitted in real time,and the transmission efficiency and reliability are reduced.To solve problems caused by wired transmission,a new wireless transmission method is proposed in this paper.Based on the principle of electromagnetic induction,the bidirectional wireless transmission between the guide head and MWD is realized in a non-contact mode,and a set of downhole wireless transmission sections is developed.The main content is described as follows:(1)The paper introduces related basic theories of downhole wireless transmission and designs the overall scheme of the system.Based on the principle of electromagnetic induction,the principle of electromagnetic induction signal transmission is introduced,the equivalent circuit model of the coil is designed,and the basic parameters of the coil are analyzed.All of these provide a theoretical basis for designing the overall scheme of the system.According to the actual downhole working environment,technical indicators that meet the system are proposed,and the overall system scheme is designed.The device and function of each module is selected and designed based on the index requirements respectively.(2)The wireless transmitting and receiving hardware circuit is designed to realize the wireless data transmission.Based on the main control chip STM32F103C8T7,the CAN transmitting and receiving circuit,transmitting drive circuit,receiving conditioning circuit and power supply circuit are designed.The output waveforms and noise performance of transmitting drive circuit and receiving conditioning circuit are analyzed though Multisim simulation and Tina-TI simulation respectively.The PCB of the system is designed by Altium Designer.(3)The software of downhole wireless transmission short section system is designed,and the functions of data coding,modulation,demodulation and decoding are realized.In the integrated development environment of Keil5,the code for encoding,modulating,demodulating and decoding program are written.In addition,the communication protocol that meets the CAN standard is designed.(4)This paper completes the assembly of the system,develops a set of downhole wireless transmission short-section,and conducts communication tests on the downhole wireless transmission short-section.An experimental platform for the downhole wireless transmission short section system is built,and the actual communication environment is simulated.From the perspective of temperature resistance and reliability of the system,the bidirectional data transmission and communication experiment of the designed wireless transmitting circuit is carried out.The experimental result shows that the highest temperature resistance of the downhole wireless transmission short-section is 125?,there is no frame loss between sending and receiving data,and the reliability is good.The functional requirements are all achieved,the performance is stable,and the high temperature resistance,which meets the functional requirements of the design.