Summary
It has been generally recognized that connectors (tool joints and couplings)
should have some effect on the buckling of pipe. For instance, the connector
outside diameter may be as much as 50% greater than the pipe-body diameter. As
a result, the radial clearance of the connector can be substantially smaller
than the radial clearance of the pipe body.
The analysis of buckling has received extensive attention in the last 20
years. The effect of connectors on pipe stresses has received somewhat less
attention. Lubinski (1977) 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. Bending stresses were significantly magnified by
the connector standoff. Paslay and Cernocky (1991) completed this analysis by
analyzing the pipe in compression. Mitchell (2000) extended these results to 3D
helical buckling.
Torque adds a new dimension to the buckling problem. Without torque,
buckling occurs only for positive effective axial force (compressive axial
force plus pressure effects). A pipe with applied torque can buckle in tension
(Greenhill 1883). The contact force between pipe and wellbore can be increased
or decreased, depending on the direction of the applied torque. And, of course,
pipe used in rotary drilling always has applied torque—so buckling analysis
without torque is not complete.
This paper looks at 3D buckling of pipes with connectors with applied
torque. The problem formulation is similar to Lubinski et al.’s (1962) buckling
analysis: the wellbore is vertical and straight. The beam-column equations
considered in the plane-buckling analysis are used, but now there are
deflections out of the plane. A solution for helical buckling is developed that
produces pipe sag, maximum dogleg angle, contact force, and bending-stress
magnification as a function of pipe effective axial force and torque. An
application problem is solved, and the relative effects of compressive axial
force and torque on sag between connectors, contact loads, and maximum bending
stress are examined.
Applications include the analysis of bottomhole assemblies, drillpipe,
casing, and tubing. The final results are simple enough to be suitable for
spreadsheet calculations.
Introduction
There are a number of practical design problems that involve buckling and
post-buckling analysis of tubulars in wellbores. Pipe stresses, contact forces,
length change, and maximum acceptable doglegs are strongly influenced by
buckling.
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 that of 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 (1977) 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, and Paslay and Cernocky (1991) completed this
analysis by analyzing the pipe in compression. 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.
© 2006. Society of Petroleum Engineers
View full textPDF
(
538 KB
)
History
- Original manuscript received:
2 June 2004
- Revised manuscript received:
10 November 2005
- Manuscript approved:
26 January 2006
- Version of record:
20 June 2006
View Cart
