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UpstreamOnline: Bully set to take drilling by horns

ADRIAN COTTRILL, London

The first example of a new concept of deep-water and Arctic drillship is due to appear in the Gulf of Mexico early in 2010.

The unit is smaller-than-normal in size yet offers top-of-the-range drilling capabilities

Its appearance follows a joint venture agreement signed this week between Shell Offshore Ventures and Frontier Drilling.

Known as the Bully rig, the design puts a strong but not exclusive emphasis on the so-called surface blow-out preventer (SBOP) approach.

It has been developed by Frontier in co-operation with Shell and rig designers Gusto MSC, along with Huisman-Itrec for drilling systems.

The joint venture has already placed a contract to build a first unit hulls to Shanghai and outfitting to Keppel and is rumoured to have at least two such vessels in prospect.

At maybe $350 million to $400 million, the price tag could be well below the level of outlay currently expected for a rig with such capabilities.

Using the SBOP approach, the Bully design has been evolved to drill in water depths up to 12,000 feet (3650 metres) and possibly more in the future.

In this approach, the main blow-out preventer is raised onto the rig deck itself and connects with a slimline 14-inch-diameter high-pressure marine riser running down to a simplified package on the seabed.

Alternatively, using the more conventional methods of offshore drilling, the vessel is also able to drill in water depths to 7500 feet (2300 metres) and again possibly extending further in the future.

In this case, a heavier mainstream 21-inch low-pressure marine drilling riser is deployed above a full BOP stack placed at the seabed.

At the heart of this initiative, aimed at Asia, Brazil, the Gulf of Mexico and West Africa, are the reduced weight and storage space requirements of slimline riser that come with SBOP drilling, and with no need to handle very heavy seabed packages.

The load on a vessel using SBOP in 10,000 feet of water is less than a third of the 4500 tonnes with the conventional approach, claims Gusto.

Shell says the vessel will feature an ice-class hull and with a sharp bow, although the first unit appears destined for the US Gulf, at least initially.

Speaking about the general design at last week’s DOT conference in Stavanger, Gusto MSC engineer Jaap-Harm Westhuis described the concept as “a new generation drilling rig with the same size and costs as a fourth or fifth-generation unit, yet with the drilling capability of a sixth generation unit” and “as small as possible without compromising operational integrity”.

Gusto’s name for the rig is the rather more prosaic PRD 12,000 MPT pressure riser drilling, 12,000 feet, multi-purpose tower.

The tower approach evolved by Huisman-Itrec uses a lighter vertical box structure containing dual draw-works with active and passive heave compensation instead of the lattice structure of a conventional derrick.

This reduced weight helps to increase the vessel’s load capability without increasing vessel dimensions.

SBOP needs a relatively high drill floor, and a key design feature of the new design is that it uses a split-level approach, placing the drillfloor at 24 metres and a utility floor 10 metres below this to support all items not needed at high level.

The vessel breadth of 32 metres is as much as 10 metres narrower than some big existing deep-water drillships, with a useful calming effect on vessel roll response.

Shell and Frontier said the length of this first 45,000-tonnes displacement Bully rig will be 188 metres. Conventional competitors range from 50 metres to 80 metres longer than this.

SBOP drilling was first adopted by Unocal in the benign waters of South-east Asia, where a large number of such wells have now been drilled. Since then Shell has pushed it into slightly more demanding deep-water environments at a few wells off Egypt and Brazil.

The deepest of these has been in water approaching 3000 metres off Brazil.

The technique has yet to be seen in the US Gulf and there may be regulatory issues to pass, but clearly Shell feels that time is now ripe in the region.

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18 October 2007 23:01 GMT  | last updated: 18 October 2007 23:01 GMT

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