TPG 500 production jack-up forms hub of Elf gas/condensate project

Computer-generated image of the Elgin Field TPG 500. The centerpiece of Britain's largest new HT/HP project will be a TPG 500 jack-up platform. Elf and its partners confirmed their choice for the Elgin/Franklin development, following a FEED study last year by the TMB Consortium.

The centerpiece of Britain's largest new HT/HP project will be a TPG 500 jack-up platform. Elf and its partners confirmed their choice for the Elgin/Franklin development, following a FEED study last year by the TMB Consortium.

TMB, comprising Paris-based Technip-Geoproduction and McDermott Marine Construction and Barmac in the UK, will deliver the E400 million process, utilities and quarters structure in September 1999, in time for first gas by April 2000. This will be the second TPG 500 in the UK Central North Sea, following BP's Harding which came onstream a year ago.

The new platform, to be located on the Elgin Field 240 km east of Aberdeen, will be bridge linked to a normally unmanned wellhead platform on Franklin, with production transported via subsea flowlines to the production jack-up. Both fields contain in total around 700MM boe, with reservoir pressures of around 1,100 bar and temperatures of 190degC. However, the HT/HP effects will have been subdued by the time product reaches the TPG 500, so no design adjustments are considered necessary.

Processed gas will head through a new pipeline system to Bacton, England for onward transmission through the UK domestic TransCo system, and the new Interconnector export pipeline to Zeebrugge. Liquids will also pass through a condensate pipeline link into the BP Forties system. Provision is also being made for a further link for another hydrocarbon stream should commercial conditions favor such action.

Elf's selection of the TPG 500 was basically cost-driven. It acknowledged that the concept employs low cost construction techniques and eliminates the need for major offshore hook-up work. Furthermore, the platform's self-installation, which allows commissioning work to be undertaken onshore, also renders unnecessary the use of heavy crane barges for module installation. The 32,000 tonne structure will be built at Barmac's redeveloped facility in Nigg, Scotland where a new graving deck will allow a free-floating wet tow direct to Elgin.

Technip-Geoproduction, which is the proprietary inventor of the TPG 500, will be responsible for project management, procurement and design of the hull, legs and foundations, including the jacking and locking system. It will also manage the platform installation.

McDermott's main responsibilities are the topsides facilities and offshore commissioning of process plant, once the platform is in position. The finished unit will have standard utilities and quarters for 69 people within the hull, with a large capacity deck for production equipment. Normal production rates should be reached during the fourth quarter of 2000, peaking at 470 mcf/d of gas and 150,000 b/d of liquid.

Harding, which is an oil production platform, sits on a concrete base used for crude storage. The Elgin/Franklin facility, however, will be secured to the seabed by steel piles driven in directly from the TPG 500. Distance between the legs will be identical to Harding's, but there will be 20% higher lifting capacity, due to the new platform's larger hull.

According to Pierre-Armand Thomas, Technip-Geoproduction's vice-president, Engineering and Projects, "We can increase the jacking capacity without harming the cost significantly. Doing that on a conventionally designed platform would have drastically increased the scope of the project."

TPG 500s can operate in 150 meters of water in two basic ways - either as a central PDQ unit with up to 32 wellheads, mainly for marginal field development. Or alternately, as a tender drilling and production platform linked to a wellhead facility, where well numbers exceed 32. In either mode it can be withdrawn and reused at the end of the field's life, minimizing decommissioning costs.

The partnership with McDermott for this concept is confined to UK waters. According to Thomas, co-operation so far on Harding and the Elgin/Franklin FEED has been very good. "We know each other, we have the same management methods and that helps save money."

There have been no takers yet in the Norwegian sector, where the partner is HMV. "Personally, I think there will be a slot for TPG 500s," says Thomas, "both in the Norwegian Sea and Norwegian North Sea. It depends on the availability of local yards."

Nor has a field been secured so far for the TPG 3300, a deep draft semisubmersible version of the TPG 500, capable of working from 3,300 ft of water. However, numerous oil companies have approached Technip-Geoproduction about the concept, says Thomas, which is aimed initially at calm environments such as the Gulf of Guinea. Like the TPG 500, it can operate in different production and drilling modes. It also retains the latter's jacking and locking principles, thereby avoiding the need for a deepwater fabrication quay. Once built, it can be wet towed to its field via the floatover method.

The basic TPG 3300 concepts comprises a water-tight deck, three to four columns with storage for up to 800,000 bbl, and a hollow pontoon. Dry wellheads can be accommodated on the deck, as with a TLP, due to the platform's proven hydrodynamic motions. However, the mooring spread, comprising 12-16 lines arranged symmetrically around the platform, is less complex than a TLP's spread. Configuration is more flexible, allowing a certain leeway with the platform's deck load.

For platforms with lighter decks, Technip-Geoproduction continues to offer its Unideck TPG installation, which involves floating the deck over the jacket, then mating the two through a combination of barge ballasting and substructure jacking. This technique was effected successfully last year on the Cobo and North Field platform installations.

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