Implementation of the ellipse algorithm to process caliper log data

Abstract

A new procedure to process caliper measurements of wellbore radii to indicate the locations of damage(s) in the casing which may occur as a result of drilling, tripping equipment in and out of the wellbore, corrosion, etc and locations of scale precipitation is proposed. In general, to identify the location of the damage in the casing, a caliper survey tool is lowered into the wellbore to measure radii of the casing. The current algorithm used to process, called the vector sum, assume the casing to be round. Since the tool may not be perfectly centered in the wellbore, the measurements are corrected for eccentricity. However, this process introduces errors since the casing may be ellipse fit, uses an elliptic rather than circular, especially when the casing is under stress and strain of different magnitudes. The new method proposed in this paper, called the ellipse fit, uses an elliptic equation to fit the data via least squares fitting. The location of casing damage or scale precipitation can be found by comparing the measurements with the ellipse fit. Caliper measurements at different times help us identify development of casing damage or scale precipitation. By comparing measurements of radii at different times, the location of casing damage or scale precipitation can be pinpointed. Synchronization between different measurements must be performed since each measurement may start at a different position. This can be done by rotating the positions of the radii until there is a match between radii of the two runs. Being able to identify the location of casing damage or scale precipitation enables us to make necessary plans for well repair.