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Did You Know...

Did you know that Galvotec Anodes protect the World's first production Spar being used as a base for well production operations located just 135 miles southeast of New Orleans in The Gulf of Mexico?

Oryx's Neptune field is located in Viosca Knoll block 826, approximately 135 miles south-east of New Orleans, in the Gulf of Mexico. The water depth ranges from 1175ft in the north-west corner of block 825, to 3,225ft in the south-east corner of block 870. To develop the field, Oryx used the world's first production spar as a base for well-production operations.

Oryx contracted Deep Offshore Technology (DOT) and their consortium members, J Ray McDermott, as the installation and topsides contractors and Aker Rauma Offshore, for the design and fabrication of the hull and mooring system.

The spar supports a three-level integrated deck above the top of the hull, consisting of a clear workover deck, a mezzanine production deck and a main production deck. Deck elevations are 116ft, 93ft and 71ft, respectively. A two-stage, three-phase separation system is used to produce the wellstream. Platform power is provided by three turbine generator sets, each rated at 900kW. The wells, pre-drilled with a semisubmersible, will be completed with a 1000hp portable platform workover rig, placed temporarily on the spar. The wellheads are located in the centrewell, between the workover deck and the production deck levels.

The spar hull of the Neptune was fabricated in 17 sections at the M�ntyluoto Works indoor assembly hall in Pori, Finland. It is essentially a 72ft-diameter cylinder, which is 705ft long with a draft of 650ft. It weighs 12,895t. A 32ftx32ft� centrewell inside the hull accommodates 16 buoyancy-supported risers, grouped in four rows of four.

Buoyancy tanks extend from the cellar deck to the bottom of the variable ballast tanks, 220ft below the waterline. It is subdivided by four vertical radial bulkheads and horizontal decks into smaller watertight compartments.

The oil is exported by six oil transfer pumps, each rated at 6,000b/d. Its two compressors can deliver 30 million ft�/day gas, at 1700psi, to the pipeline. The oil and gas are exported by separate 8in lines, 17.5km to the north, to the CNG new fixed platform on Main Pass block 225.

On the sea floor, the wells are arranged in two parallel rows, which are 105ft long and separated by 20ft, so that the wells are spaced 15ft apart in one direction and 20ft in the other. By adjusting the mooring lines, the spar can be positioned so that the riser is between the rows, while the riser is being run.

The spar is held in position by a six-line mooring. Securing each mooring leg to the seafloor is an 84in-diameter by 180ft-long pile. This is connected to 220ft of 4,3/4in chain, 2,400ft of 4,3/4in jacketed spiral-strand steel rope and 1,050ft of 4,3/4in chain, leading through a fairlead, to a chain jack at the spar's deck. Breaking strengths for the 4,3/4in wire and 4,3/4in chain are 2,750kips and 2,846kips, respectively.

The hull was transported as two sections, 390ft and 315ft in length, on-board the heavy-lift vessel Mighty Servant III. They were floated together and aligned, before the final girth seam weld was completed by Litton Ingalls Shipbuilding.

After the spar hull was upended, the pre-installed mooring lines and export pipelines were lifted from the seafloor and attached to the spar hull, using a specially designed installation-winch system. The production deck was then transported offshore on a 300mx90mx20m material barge. The lift weight of the production deck was 3,200t. The lift used for this was a typical four-point lift, utilising 12inx92ft slings.