Subsea production debut for Doris on Libya-Italy project

Platform design is one of Doris Engineering's best-known strengths. Its recent track record includes the South Pars 6, 7, and 8 projects in the Persian Gulf and Bongkot Phase 3C in Thailand.

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Platform design is one of Doris Engin-eering's best-known strengths. Its recent track record includes the South Pars 6, 7, and 8 projects in the Persian Gulf and Bongkot Phase 3C in Thailand. Here, two new platforms have been added, helping to sustain gas production at 550 MMcf/d. Doris has also modified existing platforms to strip out CO2 for the first time.

But conventional platform prospects are increasingly limited. The global trend toward subsea developments – not just in deepwater – necessitated a change of direction for the company. The big breakthrough came in 1998 with the award of the Girassol riser towers engineering contract, under a joint venture with Stolt Offshore and Bouygues Offshore. This was followed by an FPSO topsides/turret/mooring project, also for Total, in more conventional water depths off Libya.

Doris is now extending its capabilities further with another Libyan field development. It is part of a consortium with Saipem and Cameron responsible for the Bahr Essalam (formerly NC41) subsea production system, in 150 m water depth. This is a component of the $4 billion Western Libya Gas Project, an onshore/offshore development operated jointly by Agip and Libya's national oil company. Doris' scope relates to two subsea fields, 4 km apart, which will be tied back 21-km to a processing platform in 180 m of water.

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Projected 3D image of one of the Bahr Essalam subsea manifold/templates.
Click here to enlarge image


Subsea and platform gas will be commingled, processed, and transported through a 36-in. pipeline to a coastal terminal at Melitta, 100-km distant. There, the gas will be further mingled with onshore production before being compressed and exported north across the Mediterranean to Italy via a 32-in., 540-km line in waters to 1,100 m deep. Onshore gas is due onstream in September 2004, followed by offshore production in spring 2005.

Doris and Saipem are working together on a risk-sharing basis, and they are responsible for 60% of the subsea production system. The full scope comprises the engineering, procurement, construction, and installation of:

  • Two 100-metric ton pre-drilling templates and two 750-ton six-well protective structure manifolds (PSMs), and two umbilicals and subsea installations
  • Twelve wellheads, 12 christmas trees, and workover and production control systems to be supplied by Cameron subsidiaries in the UK, France, and Germany.

The consortium was awarded the ¤130 million contract last August, and Saipem vessel BOS 355 installed the two templates over three days this January. Development drilling began on March 12. Semisubmersibles Dolphin and Foramer are booked to drill 11 wells, including some long deviated sections. They will also drill four piles at each of the manifold locations.

Both PSMs will be installed on the templates next January 2004. The PSMs are an adaptation of a design used on Agip's Thelma project (the operator's choice) in the UK North Sea in the mid-1990s.

All piping is inconel-clad or solid inconel to cope with the sour gas content. Rossetti Marino is fabricating the PSMs in Ravenna, Italy (it was also responsible for the templates), and these will be shipped offshore with valves, jumpers, and other control equipment. Subsequently, the same rigs will install production guide bases and christmas trees. In July 2004, Saipem will install and test the 11 tie-in spools that will link the guide bases to the manifolds, with flexible umbilicals, still to be awarded, arriving the following month.

Saipem and Cameron will manage final commissioning of the subsea production system on the platform in January 2005. Saipem is also responsible for installation of all infield and export pipelines, while ABB has the overall offshore and onshore control system contract. Hyundai is building the platform.

According to Doris Director Michel Deguen, this is the company's second template job following a study for Total's Dalia project off Angola. One of the key issues on Bahr Essalam has been devising access for ROV intervention, he says. "But the main challenge has been the schedule. We have had to coordinate our program with that of the drilling contractor and the other partners. In this case, there are around 20 different components that have to be tied in."

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