Abstract

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

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

The tests were performed in a 2020 mMD research well, with a build-up and 60° tangent geometry. Various configurations of a tapered string with 5" and 3 1/2" drill pipe, as well as drill collars were used. A novel approach was using a high accuracy continuous gyro to measure the string geometry changes (i.e. buckling), and both downhole and topside tension devices were applied to measure weight transfer.

Several datasets recording buckling and weight transfer were obtained; the gyro measurements of drill pipe geometry changes clearly demonstrated the onset and type of drill pipe buckling.

Weight transfer was also measured under different buckling states and demonstrated that lockup occurs before reaching a helically buckled state. This might alter operational practice regarding design of running strings.

The results have been compared with predictions from buckling models, and necessary model enhancements suggested.

The work has potential to improve buckling and weight transfer models. The potential outcome will be more accurate prediction 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.

Introduction and test objective

Many years of drilling operational experience has shown that a better understanding of the mechanisms of weight transfer and drill pipe buckling is needed. In particular, design of running strings for liners has been based upon simulation programs, with limited chance of verification of actual results. In order to enhance the understanding of sinusoidal and helical buckling, and drill string lockup effects, full scale tests were planned with the aim to verify or challenge the existing buckling models, and ultimately to enhance these.

The tests were performed for evaluation of the drill string buckling models that exist in the industry today. The plan was to put high weight down on three different string-setups and measure the DP geometry with continuous gyro while keeping constant weight. The test well is about 2020 mMD deep and has a vertical, build-up and tangent profile, as shown in Figure 1. The plan was to buckle the drill pipe in each of these parts. A down hole WOB sub was placed at the bottom of the interval in question, hence shifted from TD to end of build and then to end of the vertical part. This paper focuses on the tests and some selected results. Future paper(s) will focus on mathematical impact on simulation models.

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