The slip joint (SLPJ) is an expansion/contraction compensating tool. It accommodates any changes in string length caused by temperature and pressure during a downhole test.
The SLPJ has two distinct parts: an outer housing and a moving inner mandrel. Its rugged design incorporates three main sections. At the top is a splined moving mandrel that allows torque to be transmitted through the tool. Below this are two pressure chambers, one open to tubing pressure and the other open to annulus pressure. The tool is hydraulically balanced and insensitive to applied tubing pressures. The dynamic seals in the balance chambers are dependable chevron V-seals.
Testing SLPJs have a stroke of 5 ft; the total number of SLPJs required depends on well conditions and the type of operation. For a standard test at 10,000 ft, the use of three SLPJs is normal. For tests for which injection or stimulation is planned, the associated cooling can cause a large amount of string contraction, and four or five SLPJs may be required to compensate for string movement during operations.
A special clamp securely joining the mandrel and the housing of the SLPJ is added for safety considerations for when the tool is handled at the surface.
SLPJs make it easier to space out the tubing-conveyed perforating guns when testing is done from a semisubmersible.
Note: An SLPJ is not required when the CERTIS high-integrity reservoir test isolation system is used.
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