Tubing movement and stress behaviour are a function of the well temperatures and pressures: The changes in temperature will cause the tubing to expand and contract.
For example, 10,000 ft of tubing suspended in a well will shorten by 16.6 inches with a temperature drop of 20°F. Pressures inside and outside the tubing above the packer act on the differential areas, changing the tubing length according to Hooke's law. The differential pressures between the inside and outside acting on the cross-sectional area of the packer bore at the tubing seal causes helical buckling. The pressure differential between the inside and outside of the tubing has a balancing effect. The tubing diameter increases as the internal pressure exceeds the external pressure, the result is that the tubing length decreases. The opposite is true if the annulus pressure exceeds the tubing pressure.
If tubing movement is restricted, compensating forces will be generated in the tubing string.
If tensile stress is high, consider using latched packers to carry some of the load. If compressive stress is high, pull tension at tubing hanger, or use moving seal assemblies with packer so that tubing is always in tension.
Tubing Movement compensation
Two methods are generally used
- Landing the tubing in tension/compression: This method is limited by material strength. Landing and spacing procedure is critical and often difficult achieve.
- Allowing free movement of subsurface seals: Locator tubing seal assemblies and seal receptacles can compensate for length changes. Ensure that the sealing elements do not leave the polished bore or mandrel. Landing and spacing is less critical.