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Summary

Drillpipe buckling affects the industry in many operational aspects, like motor sliding problems, liner running, or weight transfer for downhole equipment activation.

The authors believed the existing nonrotating buckling theories applied in drilling software needed challenging by physically measuring buckling in a realistic setup of well geometry and drillstring sizes and comparing the results with the buckling theories.

The tests were performed in a 2020 m measured depth (MD) research well, with a buildup and 60° tangent geometry (Aas 2008). Various configurations of a tapered string with 5- and 3½-in. drillpipe as well as drill collars were used. The tests were performed without torque or rotation being applied to the drillstring.

A novel approach was using a high accuracy continuous gyro to measure the string geometry changes (i.e., buckling) as function of axial load. Both downhole and topside tension devices were applied to measure weight transfer.

Several data sets recording buckling and weight transfer were obtained. The gyro measurements of drillstring geometry changes clearly demonstrated the onset and type of drillstring buckling. Weight transfer was measured under the different buckling states and demonstrated that lockup occurs before reaching a helically buckled state. This might alter operational practice regarding the design of running strings.

The results have been compared with predictions from standard buckling models. Necessary model enhancements are suggested.

The work has potential to improve buckling and weight-transfer models. The potential outcome will be more accurate predictions for sinusoidal and helical buckling and their effects on weight transfer. Ultimately, this will lead to better decision making and understanding in drilling and completion operations.