Effect of Tool Joints on Contact Force and Axial-Force Transfer in Horizontal Wellbores

Summary An experimental study has been conducted to investigate the effect of tool joints on the buckling/post-buckling behavior of drillpipes constrained in straight horizontal wellbores. Buckling/post-buckling behavior of drillpipes has traditionally been investigated with continuous pipes. To our knowledge, this is the first time the effect of tool joints is included in such a study. The U. of Tulsa Drilling Research Projects experimental buckling facility has been used to carry out the desired experiments. Axial loads at both ends of the pipe and contact forces at the tool joints were measured. Changes in the drillpipe configuration were also investigated visually as the axial load increases. Some of the new findings of this study can be summarized as follows. Sequential occurrence of buckling/post-buckling configuration of jointed pipe is similar to that of continuous pipes, reported previously by various investigators. In other words, in both cases, the pipes buckle first laterally and then helically as the axial compressive load increased. 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) of approximately 20%. The use of tool joints improved the efficiency of the axial load transfer by approximately 40%. The results of this study will help to improve the design of operational parameters for drilling with jointed pipes as well as with coiled tubing (CT). In particular, improved axial-load transfer performance would allow drillers to use a higher weight on bit and, consequently, faster and possibly less costly drilling.