Platform Removal Project – North Sea

Case Study

Summary

p1040297_220 Proserv Offshore were awarded a contract in March 2008 by SMIT to carry out a cutting work scope consisting of; internal sub-sea-bed pile cuts (48" x 4), internal sub-sea-bed cut on caisson (30"x1) and drilling of 12" lifting pin holes through the pile cans and piles.

Proserv Offshore mobilised equipment 10 days ahead of schedule on the 5^th of June due to offshore preparation being improved through the use of a heave, compensated gangways, and increasing workable days. The jacket was delivered to inshore location on 1^st July, during this time we required 5 working dayshifts to complete their work scope.

Internal Pile Cutting

Once the soil plugs had been removed - using an airlift tool (compressor and high volume water jetting) a runner gauge was used to confirm a sufficient amount of soil plug had been removed.

Proserv Offshore then deployed their internal pile cutter (IPC) into the first pile and lowered to cut depth (Ref 1). A fixed length of rigging was used to ensure the cut was at -6.5m. Once the tool was at depth the IPC hydraulic rams were actuated to centralise and secure the tool. Cutting assembly within the IPC was then moved from within the IPC out to the inside of the pile wall. A 360°"wash around" was carried out on each internal cut to clean and carry out a final function test. Internal pile cutter performed as required, with cutting rates as follows; 2"wt x 48"Ø piles and 1"wt x 30" Ø cut in 70 and 30 minutes respectively.

Equipment Used

JetCut System (Water abrasive cutting system)
Internal pile cutter with digital encoder
High pressure pump
Hydraulic Power Pack
Hose Reel
Workshop container
Abrasive container
Deployment frame

12" Hole Cutting

Machining of 12" Ø lifting pins through the pile can and pile (required for lifting pins - Ref 2) was done using Proserv Offshore's DrillPin - ensuring holes were opposed at 180°. Offset Rigging was used to account for the batter angle of the jacket legs, this made deployment easier. A simple rigging arrangement with ratchets and foundry hooks (Ref 3) allowed the levelling and orientation of the tool on the pile can.