A Fault-Tolerant Integrated Borehole Trajectory Location Method Based on Geomagnetism/IMU of MWD

In the oil industry, directional drilling technology plays a significant role in oil-gas exploration. The key to success of directional drilling technology is locate the borehole accurately using measurement while drilling instruments. Measurement While Drilling(MWD) technology has the problems of data loss and gross error in complex down hole environment. Aiming at the problems that gross error and data missed consequences the accuracy of positioning calculation seriously, this paper presents a method of fault-tolerant integrated borehole trajectory location based on geomagnetism/IMU of MWD system. Firstly, the geomagnetic survey system is established to locate the borehole position based on tri-axis fluxgate and tri-axis accelerometer. The Inertial Measurement Unit(IMU) calculates the borehole trajectory at the same time. Then, the fault-tolerant judgment mechanism is introduced to discriminate and evaluate data loss and gross error of measurement parameters. Furthermore, Kalman Filter algorithm is implied to construct fault-tolerant integrated borehole trajectory positioning system. Finally, the simulation experiment is performed on the drilling experimental platform. The experimental result shows that the fault-tolerant integrated borehole trajectory positioning system can detect data loss and gross error effectively. In addition, the location precision of the fault-tolerant integrated positioning system can be maintained within 1 meter when the time of data missed and gross error state lasts for 6min respectively. From the simulation experiments, comparing with the position calculation of pure geomagnetism, and the method of integrated MEMS and geomagnetism, the precision of the fault-tolerant integrated location calculation is improved by 68.7% and 62.8% respectively.