An experimental study has been conducted to investigate the effect of tool joints on the buckling/post-buckling behavior of drill pipes constrained in straight horizontal wellbores. Buckling/post-buckling behavior of drill pipes has been traditionally investigated using continuous pipes. To our knowledge, this is the first time that the effect of tool joints is included in such a study.

The University of Tulsa Drilling Research Projects experimental buckling facility has been used to carry out the desired experiments.

Axial loads at the both ends of the pipe and contact forces at the tool joints were measured. Change in drillpipe configuration was also investigated visually as the axial load increased.

Some of the new findings of this study can be summarized as follows:

  1. Sequential occurrence of buckling/post buckling configuration of jointed pipe is similar to that of continuous pipes that have been reported previously by various investigators. In other words, in both cases, the pipes buckle first laterally, and then helically as the axial compressive load increases.

  2. The presence of tool joints does not affect the critical lateral (sinusoidal) buckling load significantly. However, it increases the critical load causing helical pipe configuration (helical buckling) by about 20 %.

  3. Efficiency of the axial load transfer is improved by about 40 % with the tool joints.

Results of this study will help to improve the design of operational parameters for drilling with jointed pipes as well as using coiled tubing. In particular, improved axial load transfer performance would allow drillers to use higher weight on bit and consequently faster and possibly less costly drilling.

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