A Self-Calibration Method for Static and Dynamic Near-Bit Well Inclination Measurement

With the depletion of oil and gas resources and increasing exploration difficulty, dynamic well inclination measurement has become increasingly important. Near-bit dynamic well inclination measurement can improve borehole trajectory calculation accuracy and drilling efficiency. However, when the well inclination measurement module is installed eccentrically, installation errors are easily introduced. Additionally, during drill collar rotation, all three-axis accelerations are affected by centrifugal acceleration. These factors collectively impact the accuracy of well inclination measurement. Current dynamic well inclination measurement methods primarily focus on extracting gravitational acceleration while often neglecting the influence of installation errors on gravitational acceleration. In this paper, a triaxial-acceleration well inclination measurement module based on a single quartz flexure accelerometer and a dual-axis MEMS accelerometer is designed. The scale factor, zero bias, and non-orthogonal angle of the triaxial acceleration are calibrated using a hybrid ellipsoid and Levenberg–Marquardt method. A self-calibration algorithm for static and dynamic well inclination measurements based on multivariate linear regression is proposed, which simultaneously solves for installation errors and actual well inclination. The installation-error calibration was independently verified against a calibrated standard high-precision three-axis turntable (±0.01°), with an inclination error below 0.1° at nominal inclinations ranging from 0° to 90°. In the rotational tests, covering inclinations ranging from 5.36° to 89.64° and rotational speeds in the range of 30–150 r/min, the well inclination error is within ±0.18°. Field test results show that the near-bit inclination follows the same trend as the MWD survey, with a mean absolute error of about 0.2°.