Content of PetroWiki is intended for personal use only and to supplement, not replace, engineering judgment. SPE disclaims any and all liability for your use of such content. More information

# Combination completions

A combination completion consists of:

• More than one size of tubing
• More than one size of casing
• Two or more fluids in the tubing and/or annulus
• One or more of these.

The tubing and packer selections in combination completions must consider the impact of the multiple fluids, tubing, or casing.

## Calculation models

Hammerlindl[1] presented a method for solving problems with combination completions. His paper in particular covered two items not previously addressed by Lubinski et al.[2] He includes a direct mathematical method for calculating forces in uniform completions in which tubing movement is not permitted and a method of handling hydraulic packers is set with the wellhead in place.

There are several computer programs available today, modeled after Hammerlindl’s methods, that can easily calculate the length changes and forces generated by changes in temperature and pressure within the wellbore. These programs not only determine critical length changes but also the stresses generated on the tubing string and packer. The use of such programs is recommended.

## Tubing/packer forces on intermediate packers

Intermediate packers are an integral part of the tubing string. Examples are dual packers and single-string selective-completion packers. The packer-to-tubing force on the intermediate packer is needed so that wells can be treated through the tubing string. Without proper design, it is possible to shear the release mechanism in the intermediate packer(s) or permanently corkscrew the tubing between the intermediate packer and lower packer, either of which would result in an expensive failure of the completion or workover.

Hammerlindl[3] wrote an extension of his[1] and Lubinski et al. 's[2] earlier works that developed a theory required to solve for the intermediate packer-to-tubing forces. The calculation procedure regarding pressure effects requires working the problem from the lowest packer to the surface in sections. The first section is the tubing between the bottom and second packers. The second section is the tubing between the second and third packers (or the surface if there are only two packers). The procedures are the standard ones for uniform completions. The only changes are those to determine the changes in length as a result of applied forces on the intermediate packers; in addition, the actual and fictitious force-calculation procedures are modified. After the results of each section have been resolved, the sections must be looked at as a whole to determine the net results on the packer(s). Interested readers are referred to Hammerlindl’s 1980 paper[4] for additional information on the nebulous fictitious force of Lubinski et al.[2]

## References

1. Hammerlindl, D.J. 1977. Movement, Forces, and Stresses Associated With Combination Tubing Strings Sealed in Packers. J. Pet Tech 29 (2): 195–208; Trans., AIME, 263. SPE-5143-PA. http://dx.doi.org/10.2118/5143-PA.
2. Lubinski, A., Althouse, W.S., and Logan, J.L. 1962. Helical Buckling of Tubing Sealed in Packers. J. Pet Tech 14 (6): 655-670. SPE-178-PA. http://dx.doi.org/10.2118/178-PA.
3. Hammerlindl, D.J. 1980. Packer-to-Tubing Forces for Intermediate Packers. SPE J. 32 (3): 515-527. SPE-7552-PA. http://dx.doi.org/10.2118/7552-PA.
4. Hammerlindl, D.J. 1980. Basic Fluid and Pressure Forces on Oilwell Tubulars. J. Pet Tech 32 (1): 153–159. SPE-7594-PA. http://dx.doi.org/10.2118/7594-PA.