Annular Swivel Sub

For mechanically cutting wellheads and casing strings, perforation needs to be carried out under complete pressure control to relieve possible overpressures in annular spaces. Perforating the casing before cutting begins often takes a minimum of 3 to 5 h per string, and closing the annular preventer around the string results in considerable wear to the annular preventer sealing element.

To prevent lost time in plug and abandonment (P&A) without wearing out the sealing element, the annular swivel sub combines annular pressure release with casing cutting operations. This swivel sub saves rig time without wear to the sealing element by giving the casing cutting string a static interface and allowing rotation internally.

Swivel sub operation

The annular swivel sub is an integrated part of the string, spaced out to be positioned at the level of the sealing element. It is a rigid tool designed to resist collapsing forces applied to the routing sleeve by the hydrostatic mud column and the closing force from the sealing element.

Before the rotation and cutting operation starts, the sealing element is closed around the rotating sleeve of the annular swivel sub. The kill line is opened to record and maintain full pressure control, and the wellbore is fully closed in, safeguarding against possible overpressure between individual casings.