Reeled rigid riser installation can cut Roncador development costs

Service life not affected by reeling

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DSND's newbuild deepwater pipelay vessel Skandi Navica which was due to be delivered late last year, is to install two steel catenary risers in water depths in excess of 1,000 meters on the Roncador Field in Brazil.
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A new method for installing steel catenary risers in deepwater has been launched by DSND, which will use it for the first time to install two steel risers on Petrobras' Roncador Field in Brazil in early 2000. DSND officials say the reel method of installing rigid steel risers offers oil companies substantial cost reductions, compared with the flexible risers which currently dominate in this market.

The development, which DSND carried out in cooperation with Norsk Hydro and DNV, involved a long series of material and welding tests to document the impact of reeling on the steel pipe, and its likely effects on the expected riser life. It was established that the steel pipe was not impaired by being reeled, nor was its service life affected - in fact, it might even be enhanced due to improved conditions for onshore welding of the joints, compared with offshore.

The use of steel risers in deepwater presents a number of benefits, notably with respect to price. A typical price is NKr 1,000-2,000/meter (excluding installation), compared with a price for flexibles of more than 10 times as much, according to DSND. The company also claims improved reliability and increased ability to resist implosive pressures for steel risers. However, the economic benefit largely disappears if the riser joints have to be welded together on the installation vessel, and for this reason, the use of steel risers in deepwater has been limited thus far.

Cost breakthrough

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KS 3000, a recent addition to the DSND fleet, is a multipurpose vessel specifically outfitted to install flexible pipelines up to 1,000 meters of water. It is shown working off Brazil, where it is on long-term charter to Petrobras.
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The reel method of installation should therefore represent a breakthrough in cost terms. On the Roncador Field, with water depths of 1,000-1,400 meters, DSND calculates that it will provide a potential savings of NKr 50-75 million per well. If used for the entire development, it could entail potential overall savings of NKr 1-1.5 billion.

Another engineering innovation from DSND is a weight-saving deepwater subsea manifold which Petrobras is to install on the Enchova Oeste Field. Weight is reduced by around 30% - the Enchova Oeste prototype weighs 120 tons - by taking away all the valve actuators except one that is moved from valve to valve as required. Relocation of the actuator and valve operation is performed by ROV.

In 1999, DSND laid some 120 km of infield pipelines on Roncador. The pipelay was successfully completed in July without a technical failure, says DSND CEO Gunnar Hirsti. However, other problems were experienced, which caused delays. Final commissioning took place in November.

These lines were laid by Fennica, which has since had its pipelay equipment transferred to Skandia Navica and will revert to general subsea construction duties. For the time being, along with its sister-ship Nordica, it has been handed over to the Finnish marine administration (the owner) for winter icebreaking duty.

The company has a third offshore support vessel (icebreaker optional) on long-charter from the Finnish coastguard. This is Botnica, a light well intervention vessel which has so far found little take-up for its specialty, due to market conditions in the oil industry.

But as rig rates now move upwards, and the number of subsea wells climbs inexorably, Hirsti is optimistic that Botnica will find well intervention work. A test program will hopefully be carried out for an oil company this year.

He also looks forward to recovery in the North Sea, where the UK market in particular has been terrible over the last year or so. "The North Sea market has changed completely, from a focus on topside engineering and construction to being a complete subsea and floater market," he says. This trend, which can be seen around the world, is a development that should benefit DSND, which in the first three quarters of 1999 had a pre-tax loss but at the end of that period a solid NKr 3.8 billion orderbook.

Brazil market

Brazil has become DSND's most active theater of operations. "We believe Brazil will be the biggest offshore market for the next five years," says CEO Gunnar Hirsti. "It calls for front-end technology which can easily be transferred to the North Sea."

DSND sees the core area for its pipelay and subsea construction activities as the Atlantic rim, and is also bidding for work in the Gulf of Mexico and West Africa.

Two years ago, DSND acquired the Brazilian company Consub - now DSND Consub - and operating revenues have risen from $30-40 million to around $200 million this year, Hirsti pointed out. The latest addition to DSND's fleet, pipelay vessel Skandi Navica, will be based in Brazil. The newbuild vessel, nearing completion in November, is a reelship capable of laying rigid and flexible pipe up to 18-in. in diameter, in water depths, depending on load factors, of up to 2,500 meters. With a load capacity of 2,500 tons, it has the greatest flowline capacity of this kind in the market to date.

The new vessel brings DSND's pipelay fleet up to three. The other two vessels are KS 3000, which was part of its' acquisition of Hays Ships last autumn, and can lay flexible pipe in water depths up to 1,000 meters, and Lochnagar, a chartered vessel which lays flexible pipe in conventional depths. These two vessels are working on long-term charters for Petrobras.

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