A UK North Sea oil platform, with 45 wells, undergoing full platform decommissioning. Many of the conductors had severe integrity issues and were held together with grouted sleeves, bridle clamps and brace clamps. These devices could not pass through the platform module support frame so had to be removed underdeck.
The client sought to progress with the time-consuming process of removing the conductors and their various apertures off the rigs critical path. The solution, to rig up a WellGear 460k P&A unit next to the derrick and engage in Phase 3 abandonments, whilst the Rig continued with Phase 2.
Initially targeted the wells with the worst integrity issues, those with Talon connections. The P&A unit would cut off the wellheads, recover the 13-3/8" casing and 20" casing and finally the 30" conductor along with the clamps and sleeves.
Due to the threat of the the Talon conductors failing, the conductors could not be left self-supporting so a drill pipe support string was used in hole. Furthermore, because of the Talon connectors, the conductors had to be pulled in compression rather than in tension.
Due to difficulty on the first phase 3 work, completed using the rig, the decision was made to cut the well heads off.
After clean up pumping ops, when required, the 13-1/8" and 20" casing were cut 2 - 3ft below the wellhead using an internal cutter. The wellhead was retrieved using the platform crane.
The 13-3/8 " and 20" casing were cut at depth using a mechanical cutter and the WellGear Powerswivel. This allowed us to deliver rotation and the desired torque to the cutter without the need for the rig pumps to power a mud motor. We could use cement pump at a lower rate for circulation.
As we were pumping at a low rate we could manage return fluids despite the wellhead being removed.
Where the conductor integrity could not be trusted, the casings were recovered with up to 250ft of support string below the BHA. This allowed the team to recover the BHA to surface without leaving the conductor unsupported.
The majority of the conductors were recovered using a 'Cut and Pull' BHA ran on a 13-3/8" casing. Using a spear which could be rotated, tension for the cut waspulled locally and the cut performed at the desired depth. Keeping the spear engaged above the cut, the assembly was pulled out of hole, raising the conductor in compression.
The 30" conductor and the 13-38" casing were pinned together, using the Dual Pinning Drill, and the two strings cut in the workbasket, using the diamond wire saw. The Pinned strings were then laid on the pipe deck using the P&A unit's main 7Te winch.
Where clamps or grouted sleeves were fitted the casing was positioned at a suitable height for underdeck rope and access teams to gain access.