Shell Brunei commissions second custom-built tender semisubmersible

Smedvig's semisub tender rig West Pelaut, on which the design of the newbuild West Menang is based.

The newbuilding project has been undertaken against a five-year contract from Brunei Shell Production. The cost of the new rig, which is due for delivery in March 1999, is estimated at some $105 million, while the drilling contract revenues will be about $130 million.

The new rig, West Menang, will be based on the design of Smedvig's West Pelaut, currently the only custom-built semisub tender rig. West Pelaut became part of the Smedvig Asia fleet in 1997 upon the company's acquisition of Petrodril. It was itself built in the early 1990s to a design developed in cooperation with Shell Brunei, and since being delivered in 1994 has spent all its life working for that company. It is due to undergo a minor upgrading programme for its future work in Brunei.

The main difference between the two rigs is that West Menang will have a stronger derrick set, with one million lb design capacity rather than the more usual 750,000 lb. Shell requires enhanced drilling capacity for the development of the Iron Duke field, says Staale Roed. He sees the development as part of a general trend in the region towards drilling deeper and longer wells, creating a need for units equipped with high-torque top drive.

"It's a good contract, and we're happy with the way the relationship with Shell Brunei has developed since we came in," Roed says.

Along with the West Menang contract, Brunei Shell Petroleum has also awarded Smedvig Asia a two-year contract worth some $32 million for its T-3 tender barge. This contract will begin in January 1999.

Smedvig will maximise flexibility by making the derricks sets on the two semisub tender rigs interchangeable. In fact the new derrick set built for West Menang will first be installed on West Pelaut to enable the more demanding well work to get under way sooner.

Semisub tender rigs are more expensive to build than the tender rig barges which comprise the remainder of Smedvig Asia's fleet, but offer a series of advantages, Roed says. They enjoy enhanced motion characteristics, which significantly reduces the downtime due to weather during rig-up periods. Downtime during operations is virtually eliminated.

With ample deck space - in excess of 36,000 sq ft - and a variable deck load of 2,314 tonnes, West Menang has a large capacity for carrying equipment and supplies, thus reducing the resupply frequency and saving on supply boat costs.

The semisubmersible can perform rig-up and rig-down operations in the same position in relation to the platform as it uses for drilling - unlike the tender rigs, which have to pull anchors and change position when switching between these activities.

The semisub saves further time thanks to the lifting capacity of its 250-ton rated crane. Only 11-12 lifts are needed to transfer the derrick and drilling equipment to the platform, compared with several dozen for the tender rigs. The derrick set can be placed on or removed from the platform in 3.5 hours, and the whole drilling package can be ready for operation within 24 hours of placing the derrick set on the platform.

This is an important factor in Brunei, Roed says, where there are a lot of small platforms. The ability to move between one platform and another is therefore very important, and especially if there is only a small amount of work to be performed on a platform, for example, a one-well workover.

Equipped with top drive and power of 7,200 kW, the rig is capable of drilling the extended-reach and horizontal wells which play an increasingly important role in field development.

The versatility of the semisub tender rig goes beyond a pure drilling function. Its crane capacity, coupled with its enhanced stability, enable it to be used for lifting other types of equipment, such as helidecks or process equipment, and for construction purposes.

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