Research On Measurement While Drilling System Based On Fiber Optic Gyroscope (FOG)

Measurement While Drilling(MWD) is based on the principles of strap-downinertial navigation(SINS), which constitutes a three-axis fiber optic gyroscope andtriaxial accelerometer called inertial measurement unit（IMU）. The parameters ofattitude angle, position and velocity are calculated by mathematical platform in realtime. With oil exploration and exploitation as the background, the system is used inlong distance and continuous borehole deviation measurement occasions. From theprinciple of MWD, strapdown inertial navigation system is an alternative totraditional inertial navigation systems, and the inertial sensors included with fiberoptic gyroscopes and accelerometers substitute the traditional structure withfluxgates and accelerometers, which is suitable for the occasion with the magneticfieldinterfere. In this dissertation, a detailed analysis of the working principle andthe measurement system with types of static errors and dynamic errors is given, anddifferent kinds of methods towards error compensation are discussed. The errorcompensation is realized with the24position calibration experiments, the rate ofcalibration experiments, the temperature experiment, and the two-position rotaryclosed-loop control experiments.The study of MWD starts with the measuring principle, the measurement erroranalysis and compensation, the method of attitude calculation and the attitudedisplay. Detailed analysis and design of the experimental platform with MWD aremainly employed to complete the study that includes four aspects as follows:Firstly, a detailed description of MWD is elaborated, and the mathematicalexpressions of strapdown attitude matrix are builded, and three different kinds ofattitude solution methods that involve Euler angles method, the direction cosine lawand the quaternion method are analyzed and discussed. In the end, the quaternionmethod is choosed and employed to realize the attitude updating solution.Secondly, the topic establishs the experimental platforms of MWD, includingthe power supply module, data acquisition and processing module, the motorclosed-loop control module and communication module,and so on.Thirdly, the research focuses on the dynamic and static errors in themeasurement system, and conducts the discussion of the error compensation method,and sets up the error model of IMU. Particularly, the quadrature error compensationis proposed as a new compensation method and achieves good compensation effects.The initial alignment is executed in the static base, and the fine alignment based onthe Kalman filter algorithm is used to obtain the exact initial position of strapdownattitude matrix. It utilizes the two-position method to improve the observability of the system, in order to improve the accuracy and speed of parameter estimation.Finally, it is completed with dynamic simulation analysis and static testing ofthe MWD system, and puts forward the possiable influencing factors of themeasurement errors. Through the static position testing, the attitude angles canobtain higher measurement accuracy to meet the basic measurement indicators withMWD. Taking advantages of Labview, the design of data acquisition interface andattitude information display is finished, which has good interaction and real-timecharacteristics.