Comprehensive Analysis of Buckling With Friction
- R.F. Mitchell (Enertech Engineering and Research Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- September 1996
- Document Type
- Journal Paper
- 178 - 184
- 1996. Society of Petroleum Engineers
- 1.14.1 Casing Design, 1.6 Drilling Operations, 1.4 Drillstring Design, 2 Well Completion, 5.5 Reservoir Simulation, 1.6.10 Running and Setting Casing, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6.1 Drilling Operation Management
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While analytic solutions are available for a limited number of special load cases, the general solution of buckling with friction requires a numerical solution. This paper describes the formulation and solution of the helical buckling of tubulars with friction. An example application demonstrates many Surprising results, especially when friction forces from previous load steps are unloaded.
The buckling behavior of tubing has an important impact on well design and on production operations. For example, tubing movement due to buckling will influence seal length design, and bending stresses due to buckling may dictate tubing weight and grade. Early analysis of buckling, such as Lubinski et al. considered only the vertical well with no friction. More complicated well completions were considered by Hammerlindl, but used the same buckling model with the same restrictions. The importance of friction was recognized in these papers, e.g. Figure 4 of reference 2 shows an experimentally measured 50% error from the frictionless buckling length change, which is attributed to friction. An initial attempt to include friction in the basic Lubinski-Woods buckling model was made by Mitchell. In this work, analytic solutions to two basic problems were developed, (1) slacking off from the surface, and (2) loading upward from the base of the tubing. Analytic solutions were possible because the load application was in a single direction. While limited in application, this work showed the considerable importance of friction forces on buckling and on tubing design. For instance, friction can greatly reduce set-down force regardless of surface slack-off. More sophisticated models have been developed for buckling, but these analyses still lack the effects of friction. The model presented in this paper is a generalization of the earlier analytic model to include the effects of axial friction on tubing forces and displacements. In this numerical formulation there is no restriction on the load history.
The comprehensive friction model uses a displacement based formulation. In this formulation, calculation of displacements is used to solve the tubular stress problem instead of the seemingly easier force calculation. The primary reason for displacement calculation is that the application of the friction load requires knowledge of the incremental displacement direction. As a secondary benefit, many tubular problems require displacement boundary conditions, such as fixed and limited displacement packers or wellhead movement. These boundary conditions are not easily satisfied in a force calculation. Finally, displacement results are needed for many applications, such as tubular length changes for packer seal length design.
|File Size||318 KB||Number of Pages||7|