Lateral Buckling of Pipe With Connectors in Horizontal Wells
- R.F. Mitchell (Landmark Graphics)
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- June 2003
- Document Type
- Journal Paper
- 124 - 137
- 2003. Society of Petroleum Engineers
- 1.6.1 Drilling Operation Management, 1.14.1 Casing Design, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.6 Drilling Operations, 1.10 Drilling Equipment
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The effect of connectors on pipe buckling has only recently received attention. For nonbuckled pipe, Lubinski analyzed the effect of connectors on pipe in tension in a curved borehole, and Paslay and Cernocky extended this analysis to pipe in compression. The first analysis of buckled pipe with connectors was done by Mitchell, who developed a 3D analysis of helical buckling. These papers indicate that bending stresses are greater because of connector standoff.
Laterally buckled pipe with connectors is analyzed for the first time in this paper. It presents an analytic solution of the beam-column equations in 3D in a horizontal wellbore with pipe weight.
Pipe deflections, contact loads, and bending stresses are determined with explicit formulas. Sag between connectors is calculated so that pipe body contact with the wellbore between connectors can be determined.
Applications include the analysis of bottomhole assemblies, drillpipe, casing, and tubing. The solutions are simple formulas that are suitable for hand calculations.
Clearly, connectors should have an effect on the buckling of pipe. For instance, because the connector outside diameter may be as much as 50% greater than the pipe body, the wellbore radial clearance of the connector can be substantially smaller than the radial clearance of the pipe body. Buckling criteria, such as the Paslay- Dawson formula, depend on the radial clearance. Which radial clearance should be used? Should it be the pipe body clearance or the connector clearance? Further, there should be a measurable effect of connectors on pipe stresses for axially loaded pipe.
There is limited analysis available on nonbuckled pipe with connectors. Lubinski used the beam-column equations to analyze the effect of connectors on pipe bending stresses for a pipe in tension in a 2D constant curvature wellbore,1 and Paslay and Cernocky completed this analysis by analyzing the pipe in compression. 2 Pipe was found to be either suspended between connectors, in point contact with the wellbore, or in wrap contact with the wellbore, depending on the pipe tension. Bending stresses were significantly magnified by the connector standoff.
The next step, 3D buckling of pipes with connectors, was taken by Mitchell.3 The problem formulation was similar to Lubinski's buckling analysis for pipe without connectors4: the wellbore is vertical and straight. The beam-column equations considered in the plane buckling analysis1,2 were used, but now there were deflections out of the plane. A solution for helical buckling was developed that corresponded to Lubinski's solution for low axial compression but produced pipe sag and bending stress magnification for higher axial loads. Calculation results included connector contact forces, bending stress magnification, maximum dogleg angle, and pipe sag.
This new analysis takes the 3D buckling problem one step further. The continuous contact problem for pipe buckling in deviated wells has been addressed by several authors.5-7 To extend these concepts to connector analysis, the beam column equations are solved for a horizontal well with lateral loads on the pipe. Lateral buckling of the pipe is analyzed, with critical loads for buckling initiation determined. Equilibrium lateral deflections are determined, along with pipe sag between connectors, bending stress, and contact loads. Conditions for positive contact forces are determined and compared to buckling criteria, such as Paslay-Dawson.7
At the end of this paper is a complete nomenclature and reference list.
In mechanical engineering, buckling is usually concerned with stability. For example, The Euler column with pinned ends has a stable configuration up to the axial load8:
For axial forces greater than Fcrit, the original straight pipe solution is no longer stable, and the column may fail catastrophically. In a horizontal wellbore, the situation is different.
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