NUGGETS, North Sea Northern, United Kingdom

The Northern Underwater Gas Gathering Export and Treatment System (NUGGETS) is located in blocks 3/18c, 3/19a, 3/19b, 3/20a, 3124a, 3/24c and 3125a in the UK sector of the northern North Sea, south of Dunbar, where the water depth is 120m. The field is operated by TotalFinaElf, which holds 100% of the equity holding.

The fields lie in an Eocene production horizon and recoverable reserves are estimated at 500BCF of sales gas.

DISCOVERY

The field was discovered in July 1973, when the submersible Ocean Traveller, operated by Total, drilled well 3/19A-1B in 168m of water. The well was drilled to a depth of 2,468m and the discovery tested 12.4MMcfd of gas. Another well in the block, drilled in 1989, using the semisubmersible Benreoch, tested up to 23.4MMcfd gas at 2,180m. These two wells formed the Nugget 1 accumulation.

First oil was discovered in 1988 by Shell, during drilling in the ninth-round block 3/19B. The semisubmersible Stadrill, whilst drilling in 109m of water, predominantly found gas with some oil in the 4,100m well. This was the Nugget 2 accumulation.

In 1991, Total drilled 3/19a-4 to the west of Shell's find and tested gas at 25.5MMcfd, through a 48/64in choke, using the Sedco 706. This discovery was called Nugget 3.

In 1974, when the Total-operated wildcat 3/25a-2, drilled by the Neptune VII semisubmersible, tested 14.9MMcfd of gas, this was called Nugget 4. A subsequent well (3/24a-3), drilled to the east in 1990, also encountered gas and proved the extension of Nugget 4 into the 3/24a block.

This geology suggests that the field may extend into seven blocks.

DEVELOPMENT

TotalFinaElf Exploration awarded the EPIC contract for Phases 1 and 3 of the development (covering subsea facilities and pipelines) to a joint venture between Coflexip Stena Offshore Limited (CSOL) and ABB Offshore Systems.

The base case scope of work for Nuggets Phase 1 comprises a new manifold at Nuggets, tied back by a 40km, 12in pipeline, with a 3in MEG piggyback, to the North Alwyn platform. Two subsea wells will be installed, one adjacent to the manifold and one 3km away, connected by a 6in and 2in pipeline. Controls are provided from the Dunbar platform, via a 20km umbilical, which stretches to the manifold, then onwards up to the two wells. First gas is scheduled for mid-October 2001.

The contract included two options for additional facilities, which have just been awarded to the consortium. Nuggets Phase 3 comprises a second manifold with an adjacent well, umbilical and a 14.5km, 12in pipeline with a 4in MEG piggyback line tied back to the Phase 1 manifold.

The Nuggets Phase 2 option includes a further well, tied back 4.4km to the Phase 3 manifold by a 6in pipeline, with a 2in MEG piggyback line and umbilical.

CSOL will design, procure and fabricate the pipeline systems and perform the offshore installation and tie-in of the pipelines, umbilicals and manifolds. Installation of the system will be undertaken, starting in mid-2001.

ABB will provide the horizontal subsea trees and the control system. The umbilicals and manifolds will be supplied by Duco. The control system and umbilical installed in the initial phase will have the capacity to support the full field development, including expansions, resulting in an overall subsea step-out of 43km.