Real-Time Positioning Method for Horizontal Directional Drilling Based on Ground Magnetic Beacon

Determining the dynamic position of the drill bit is the key to the successful implementation of horizontal directional drilling (HDD). To improve the accuracy and the scope of application of HDD positioning technology, a new method is proposed to detect the position of the drill bit. A cylindrical permanent magnet with 50 mm in diameter and 300 mm height is placed on the ground as a magnetic beacon and the magnet axis is parallel to the horizontal plane. A sensors array which consists of five tri-axial magnetometers, a tri-axial accelerometer and a tri-axial gyroscope is attached to the bottom hole assembly and measures the magnetic gradient tensor of the magnetic beacon. Then, the position of the drill bit can be solved by the localization algorithm based on magnetic gradient tensor. The simulation analysis shows that. The simulation analysis shows that this method has high positioning accuracy in vertical direction and horizontal direction, and the position errors can be controlled within 1% through adjusting the beacon position, the number of the permanent magnets, the sensitive of magnetometers and the baseline distance. Besides, in the limited space of drilling tools, the longer the baseline is, the higher the position accuracy is. The outdoor experiment demonstrate that this method totally avoids the impact of the environmental magnetic field and has good practical effect. Conclusion can be made that this new method can be applied in trenchless HDD positioning with better effect and wider application range than other methods.