Effect of Tool Joints on Contact Force and Axial-Force Transfer in Horizontal Wellbores
- O.B. Duman (Turkish Petroleum Corp.) | S. Miska (U. of Tulsa) | E. Kuru (U. of Alberta)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 2003
- Document Type
- Journal Paper
- 267 - 274
- 2003. Society of Petroleum Engineers
- 1.7.7 Cuttings Transport, 4.1.2 Separation and Treating, 1.10 Drilling Equipment, 1.8 Formation Damage, 1.6 Drilling Operations, 1.7.1 Underbalanced Drilling, 4.1.5 Processing Equipment, 1.6.3 Drilling Optimisation, 1.5 Drill Bits, 1.15 Fundamental Research in Drilling
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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.
It is well recognized by the drilling industry that the occurrence of pipe buckling is of great practical importance. A slower rate of drilling (caused by poor axial-force transfer to the drill bit) and pipe overstressing (that may result in its mechanical failure) are some of the major factors contributing to the high cost of drilling.
There are a number of technical papers focused on the issues of drillpipe/CT buckling. Most are theoretical in nature and subject to a number of simplifying assumptions. Most investigators assume that the pipe is static (no rotation, no fluid flow, etc.) and continuous and that the system is frictionless.
In their classical paper, Lubinski et al.1 showed that the axial force-pitch relationship for helical pipe configuration (the so-called helical buckling) is as follows.
Eq. 1 gives the relationship between the axial force, F, and the pitch length, p, for a pipe with a bending stiffness of EI. The main assumptions made by Lubinski et al. were that the system is frictionless and the pipe weightless. Based on these assumptions, the helix pitch length is constant along the string.
Cheatham and Pattillo2 investigated the force-pitch relationship for loading (increasing compression) and unloading (decreasing compression) cases. Their solution was the same as Lubinski's for the loading case.
The authors stated that a radially inward virtual displacement is permissible during the unloading. Therefore, Eq. 1 cannot be used for this case.
Cheatham and Pattillo2 suggested the following equation for the force-pitch relationship for the unloading case.
Dawson and Paslay3 effectively simplified Paslay and Bogy's4 results to find the critical compressive load in an inclined hole that results in a lateral (sinusoidal) buckling of originally straight pipe.
in which Fcrit=the critical force required to initiate buckling and r=the pipe radial clearance.
Eq. 3 is commonly used by the oil industry for determining the initiation of lateral (sinusoidal, snaking) buckling.
Dawson and Paslay3 stated that the presence of tool joints would reduce the radial clearance and increase the critical buckling loads. Nevertheless, no experimental results have been reported to prove this.
Chen et al.5 presented their solution regarding the buckling behavior of pipe in horizontal wells. Their solution is the same as Dawson and Paslay's when the inclination angle, a, is set to 90°.
Following the principle of virtual work and the theorem of minimum potential energy, Chen et al.5 assumed that the force is constant in magnitude and direction on the virtual (fictitious) displacement from the straight to helical configuration. As a result, they obtained the following equation for the critical helical-buckling force.
in which Fhel=the critical helical buckling force.
Wu and Juwkam-Wold6 derived an expression for the critical helical buckling load as follows, assuming a linear increase in the axial compressive force.
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