A Study on North-Finding Methods for an Intelligent Downhole Inclinometer Instrument Based on MEMS Gyroscopes

The determination of borehole trajectory azimuth—particularly the establishment of true-north orientation—is critical for measurement-while-drilling (MWD) operations. Traditionally, MWD systems have relied on magnetic sensors for north-finding; however, such methods often prove unreliable within steel tubulars and high-temperature downhole environments. In this paper, a novel self-northing inclinometer instrument based on a six-degree-of-freedom MEMS inertial sensor package—comprising a tri-axial accelerometer and a high-precision gyroscope—is presented. First, the operational principles of MEMS gyroscopes and the theoretical basis of gyroscopic north-finding are reviewed. Then, the system architecture of the downhole inertial measurement module is detailed, along with specialized calibration and compensation techniques designed to mitigate high-temperature and high-shock effects. A sensor-fusion and signal-processing framework employing drift-correction strategies is proposed to alleviate the inherent bias instability of MEMS gyros The accuracy and robustness of the algorithms are validated through both simulated borehole-trajectory data and prototype field experiments, with performance metrics and error analyses provided. Finally, the calibrated and compensated MEMS-gyro solution is benchmarked against conventional magnetic inclinometers and fiber-optic gyro systems; the results demonstrate that a fully calibrated MEMS approach can achieve near-navigation-grade performance. The findings indicate that, under downhole conditions, MEMS-gyro-based north-finding inclinometer instruments can deliver sub-degree azimuth measurement accuracy, offering a compact and cost-effective alternative to traditional gyro systems.