Published on 9 July 2018
1st Saltel Patch installed from a semi-submersible rig
Set offshore (North Sea) from a semi-submersible platform without active Heave Compensator, the Patch successfully isolated a leaking coupling.
A leak was located on a coupling, in a 103/4in – 60.7 lbs/ft casing, 65 ft below tree wear bushing (leak depth was 610 ft. RKB = 533 ft. MSL).
The required solution had to be set on a semisubmersible rig giving no guarantee of accurate positioning at depth, due to the heave. The rig did not have an active heave compensation system available (to maintain the BHA at a constant depth).
A customized (6mm steel thickness) 103/4in Patch – 5m long was selected, to maximize the differential service pressure rating.
The semi-submersible rig was constantly moving up/down, (no active heave compensator) which would have resulted into the inaccurate positioning of the BHA for each expansion step and uncontrolled forces downhole transmitted to the Patch and the BHA.
The solution to such challenge was modifying the setting process by adding a no-go approximately 60ft above the BHA, landing on the tree wear bushing to position and anchor the casing patch. The tools were then POOH, and the distance between the no-go and the setting tool was adjusted for the next steps.
The downside when landing the string, is the impossibility to slack-off when the packer pulls on the no-go during the inflation. This generates a force on the Patch that can make it skid. A modification of the setting tool was implemented and tested in HQ. This modification aimed to release this tension, by transforming the Mechanical Bleed Off (MBO) safety mechanism into an expansion / slip joint with 1in stroke, in case 9 tons [20k lbs.] were exceeded.
As expected, the system activated automatically for runs #2 to #8, which participated as a good indication of the effective setting.