Summary
Hydraulic control lines are commonly used to actuate surface-controlled
subsurface safety valves (SCSSVs), and new applications include choke operation
and the control of more-complex "smart-well" completions. In general, control
lines are not subject to routine failures. However, the analysis of worldwide
completion failures indicates control lines to be a critical component of
failure. In fact, control lines and associated components, such as clamps and
fittings, are not engineered with the same rigor as the rest of the well
completion.
The first step in understanding control-line failure is predicting the loads
and stresses in a control line strapped to the tubing. Tubing movement causes
loads in the control line through stretching and bending. To a lesser degree,
the tubing is loaded by the control lines. To determine this interaction, a
calculation is performed in which the control line and the tubing are treated
as a composite, with axial displacement constrained to be the same in both.
This analysis provides the average stress state in the control line. Because
the control line is fixed at only certain points along the tubing, the
variation in stress from the average must be determined between clamps. This
paper provides the technical details for both calculations.
Several example cases based on field data are presented that give insight
into the potential problems that typical production scenarios create for
control lines.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
17 December 2007
- Meeting paper published:
17 March 2009
- Revised manuscript received:
16 April 2009
- Manuscript approved:
25 September 2009
- Published online:
25 February 2010
- Version of record:
14 June 2010
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