Research On Error Compensation Of Magnetometer Measurement While Drilling

Measurement while drilling technology refers to the technology of realizing continuous measurement of various parameters while drilling bit.At present,MWD is mainly used for trajectory monitoring and attitude calculation of downhole drill bit through magnetometer,accelerometer and gyroscope measurement data.Accelerometer and gyroscope are not affected by magnetic interference.The former compensation algorithm tends to be mature but is easily affected by vibration,while the latter has high instantaneous accuracy but has accumulated drift error.Magnetometer has strong vibration resistance and no cumulative error in azimuth.However,magnetometer signal is easily affected by the complex and changeable downhole environment and the error of drilling tool itself,so the azimuth accuracy of magnetometer involved in the calculation is greatly reduced..With the application of directional wells such as horizontal multi-branch wells and cluster wells,the azimuth accuracy of attitude calculation while drilling is increasingly required.The accuracy of azimuth has a great influence on the drilling risk and encounter probability of well trajectory,so the study of magnetometer error compensation has important research significance.There are complex and variable disturbances of underground magnetic dry,such as magnetite ore,interference from nearby Wells and magnetization of non-magnetic drill collars,may lead to abnormal magnetometer measurement signals.Based on a large number of domestic and foreign literature,this paper firstly analyzes the error characteristics of magnetometer and builds the error model of magnetometer.Considering the influence of downhole magnetic interference on the measurement while drilling,the on-line calibration algorithm and on-line filtering method for magnetometer error compensation are proposed.The main research contents are as follows:(1)The working principle of magnetometer is briefly introduced,the error characteristics of magnetometer are analyzed and the magnetic signal error model is constructed,and the error correction method of magnetometer is briefly introduced.(2)Based on the basis of the established magnetic error model,combined with the gyroscope signal,an online calibration algorithm based on equivalent rotation and improved cuckoo was proposed.The 12 error parameters of the magnetometer were calibrated and solved,and experiments show that the method is effective for magnetometer error compensation.(3)In order to make better use of the effective signal of measuring element,a magnetometer signal processing method based on cross-correlation extraction is proposed by using the same frequency period signal characteristics of accelerometer and magnetometer,which effectively reduces the signal error of magnetometer and improves the azimuth accuracy.(4)In order to further improve the accuracy of magnetometer signal,a data processing method of adaptive particle filter is proposed.The experiment proves that the method greatly reduces magnetic error and improves azimuth accuracy.21 pictures,7 tables,74 references.