Research on Wellbore Axis Alignment Calibration Method for Casing Deformation Ultrasonic Three-Dimensional Imaging Technology

This study proposes a wellbore axis alignment calibration method for casing deformation ultrasonic three-dimensional imaging technology. This method is based on the characteristic of uneven distribution of data points captured through circumferential scanning when the ultrasonic detection instrument is in an eccentric position. It utilizes the difference in arc lengths between adjacent data points to assign weighted values to each data point. Based on the weighted values of each data point, the weighted averages of the Cartesian coordinates of all data points within one circumference are calculated. The weighted average represents the geometric center coordinates of the casing circumferential curve. The eccentricity is then calculated by subtracting the origin coordinates from the geometric center coordinates. Finally, the eccentricity is used to quantitatively calibrate the wellbore axis alignment. Firstly, the polar coordinates of each data point are converted to Cartesian coordinates using the information of azimuth and distance captured by the scanning instrument. The arc lengths of the data points are calculated based on their coordinates, and the minimum value is selected as the reference. The ratio of each data point’s arc length to the reference value is used as a weighting factor to calculate the weighted average of the Cartesian coordinates. The difference between the weighted average coordinates and the origin represents the offset distance. The planar Cartesian coordinates of all data points are calibrated accordingly, achieving the calibration of wellbore axis alignment in casing deformation ultrasonic three-dimensional imaging. In this study, the two-dimensional alignment calibration was initially performed for standard circular, elliptical, and irregular-shaped casings. A total of 32 data points were selected per circumference, and the calculation results were satisfactory, with a maximum calculation error of 5.5% for the vertical axis offset of the elliptical shape. The three-dimensional alignment calibration was then analyzed. By simulating the data point of casing circumference under the eccentric condition of the detection instrument, the eccentric casing’s three-dimensional morphology was calibrated based on the alignment calibration model. Finally, the differences in morphology before and after calibration were compared and analyzed. The results showed that with an increase in the number of data points, the alignment calibration error decreased. When the data points were increased to 200 per circumference, the maximum error of the alignment calibration was less than 2%. This research method enables rapid calculation of the offset distance of the detection instrument, accurate determination of the relative position relationship of casing morphology at different well depths, and calibration of wellbore axis alignment in casing deformation ultrasonic three-dimensional imaging. It improves the accuracy of three-dimensional imaging and presents the true morphology of casing deformation more effectively.