Estimation of geomagnetic components under unknown interferences for drilling tools

Abstract

The geomagnetic components measurement directly influences the azimuth and magnetic Toolface of downhole drilling tools. Accurate estimation of the geomagnetic components is crucial for wellbore trajectory control. However, the unknown magnetic interferences caused by ferromagnetic drilling tools introduce significant errors in the estimation of the geomagnetic components. Firstly, this paper considers the constraint of a constant total magnetic field value and introduces the unknown axial interferences of the drilling tools as a new state. At the same time, parameter uncertainties and radial interferences within the drilling tools are regarded as unknown but bounded, leading to the establishment of a linear time-varying system model for the measurement system. Then, a state estimation method based on the Zonotopic Kalman filter (ZKF) is proposed for geomagnetic components and attitude measurements. The simulation results indicate that, compared to the ZKF method without considering nonlinear constraints, the method proposed in this paper effectively separates the axial interference of the geomagnetic components from the drilling tools during dynamic measurements. The root mean square errors of the estimated three-axis geomagnetic components are reduced to 0.0249 Gauss, 0.0082 Gauss, and 0.0148 Gauss, resulting in improvements in accuracy of 96.06%, 28.6%, and 14.1%, respectively. Furthermore, the root mean square errors of the gravity Toolface, magnetic Toolface, and azimuth estimation decreased to 1.8296°, 1.8294°, and 3.2898°, leading to enhancements in accuracy of 9.61%, 9.71%, and 96.37%, respectively. Finally, experimental validation confirms the effectiveness of the proposed method, providing a reference basis for dynamic measurement while drilling.