Research On Attitude Determination Of Inertial MWD

In order to improve the efficiency of oil and gas resource detection and extraction,Measurement While Drilling(MWD)requires real-time and accurate control of the drilling trajectory during drilling,and the premise of realizing precise control of the drilling tool running trajectory is to obtain high-precision drilling tool movement attitude information.Inertial MWD can use the measurement unit composed of three-axis accelerometer,three-axis gyroscope and three-axis magnetometer to measure and collect the acceleration,angular velocity and magnetic field strength data of the drilling tool,and obtain the attitude of the drilling tool through strapdown inertial attitude calculation method.Inertial MWD is completely autonomous performance,freedom to external disturbances and abundant output information.However,the environment of MWD has some harsh properties such as high temperature,strong vibration,strong impact,strong magnetic interference and so on,in addition to the error of inertial device itself,there will be a lot of interference in the drilling tool motion information collected by the measurement unit,resulting in a large error in the calculated drilling tool attitude information.Therefore,it is very important to improve the measurement accuracy of attitude while drilling.In this paper,the following aspects of attitude determination and measurement accuracy improvement of inertial measurement while drilling are studied:(1)A MWD system consisting of three-axis accelerometer,three-axis gyroscope and three-axis magnetometer is used to measure the acceleration,angular velocity and magnetic field strength of the drilling tool.The attitude angle of the drilling tool is calculated according to the strapdown inertial attitude calculation method,and the attitude error of the drilling tool is analyzed.(2)Aiming at the problem of serious distortion of MWD attitude caused by vibration interference in the measured acceleration data of drilling tools,an algorithm of MWD gravity extraction based on distribution estimation is proposed.(3)Aiming at the problem of inaccurate attitude angle measurement caused by gyro drift in the inertial while drilling measurement,a gyro drift compensation algorithm based on PI control is proposed(4)Aiming at the characteristics that the accelerometer and magnetometer data are easily interfered by the external environment and the angular velocity data has high short-term accuracy,an information fusion attitude calculation algorithm based on EKF is proposed.