In the development of the Tahoe prospect, Shell Oil Company, designed the flowlines to be dual 4" nominal lines to begin in 1500 feet of water and laid to the Bud Platform in 273 feet of water. The flowlines were to be laidsimultaneously since they were to be tied into previously laid flexible jumper lines. The flexible jumpers were retrieved, the rigid pipewelded to the ends and the flowlines laidutilizing the Reeled Pipe Method to Main Pass 252, the location of the Bud Platform, where conventional risers were installed to make the surface connection.
This paper will describes the pipe laying techniques used for this project. Specifically, the improvements in stinger design to permit lower horizontal tension loads, the use of dualpipe reels to maximize productivity, and the advantages of laying from a DP vessel.
Shell decided to utilize sub-sea technology in the development of the Tahoe Field. It Wi3S decided to pre-drill a well, install a control umbilical and lay the flowlines from the well location to an existing platform. The flowlines and control umbilical were tied into the well with the use of a Flowline Connector Assembly (FCA). The FCA was lowered and connected to the well by a drilling rig which was positioned at the well sight. Tahoe is located in 1500 feet of water at Viosca Knoll 783 and the existing platform, Bud, is in 273 feet of water at Main Pass 252.
The project consisted of laying approximately 60,500' of 4.5" × 0.438" wt, X-42 Production Line pipe and approximately 60,500' × 0.438" wt, X-42 Annulus pipe. Each flowline terminated with 300 feet of 4.5" × 0.531" wt, X-52 pipe. Both lines arc coated with Fusion Bonded Epoxy (FBE) coating as arc the field welds. Sixty-five (65) pounds of sacrificial aluminum anodes are attached to the pipe at 640 feet intervals. The plan was to recover two previously laid flexible pipe jumpers, approximately 2,()()() feet long, weld the rigid pipe to the flexible pipe and lay away from the WCII to the Bud Platform.
Because of the water depth and the complexity of the job, the DB 50 was the vessel of choice. The water depth was such that moored vessels arc difficult to work, although, there halve been some recent development to mooring systems that have increased water depths limitations. The DB 50's Dynamic Positioning (DP) system is well suited for this water depth. It was also decided to utilize the Reeled Pipe Method to install the flowlines. This would minimize the time in the field, as well as weather exposure for the construction vessel. This combination made for a very cost effectivesolution for this project.
The pipe, delivered in double random lengths, was welded and reeled onto the pipe reels at the land facilities in Morgan City, Louisiana, The pipe was fabricated into 360 feet long stalks and rolled onto the storage rack until sufficient stalks were completed to begin the pipe reeling process.
