Abstract

Subsidence in chalk fields loads casing and liners with axial compression loads and results in uneven radial loading of the pipe wall. Eventually the casing or liner will fail from plastic collapse under the stress generated by the uneven radial loading combined with axial compressive load.

Casing Slip Joints placed in the compacting zones can reduce the combined stress in the cross sections thus increasing the stress level from uneven loading that can be tolerated.

Current designs require an activation load of 150,000 lbf. to initiate closing. The effect of a slip joint will be greatly improved if the Slip Joint is able to close when subjected to a small compressive load instead of the 150,000 lbf. currently required.

A system has successfully been developed that allows the Slip Joint to be run-in and cemented in its open position and yet be able to stroke freely after a preset time.

The system uses metallic shear screws that transmit a force equal to their full cross sectional shear strength when running- in. After a pre-set time their strength will be reduced to nearly zero through controlled stress corrosion cracking.

A number of materials were evaluated and one material was tested. The internal tensile stress required for the Stress Corrosion Cracking (SCUC) process can be adjusted to achieve a predetermined and predictable time to failure.

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