HydraLift Rig concept makes deepwater debut on converted Shell semisubmersible

Artist's impression of Stena Tay with HydraLift Rig installed. [40,532 bytes]

Hydralift's HydraLift Rig made its market breakthrough last year when Stena Drilling awarded the company a NKr 300 million contract - its biggest ever - for a drilling equipment package.

Due for delivery in mid-year, the package will be installed on the Stena Tay semisubmersible drilling rig, which is being converted from the Safe Gothia flotel at the Keppel FELs yard in Singapore. Once the conversion is complete, the rig will take up a long-term contract with Shell, drilling in deepwater on the Brazilian shelf.

The HydraLift Rig is one of several developments undertaken by Hydralift with the deepwater market specifically in mind, according to Karsten Meling, export manager for the company's drilling division. New concept developments have also taken place in the company's riser tensioner technology and in large combination knuckle-boom cranes. The Stena package includes all these items, plus additional equipment.

The HydraLift Rig incorporates three ram cylinders which give it 750 tons lifting capacity over its 36-meter lifting height. It has the added advantage that if one cylinder fails and has to be removed for repair, the rig can continue working at a reduced capacity of 500 tons with the remaining two.

Another part of the Stena package is Hydralift's proven heave compensation system, which is widely used on drilling rigs and cranes. It is not integrated in the general hydraulic system. Instead, there is a separate passive and active compensator installed on the deadline side of the wireline. The end result is a simpler and more reliable system.

For Stena Tay the newly developed N-Line Drilling Riser Tensioner System, for which a patent is pending, incorporates six cylinders, each with a 50-ft long-stroke and a total capacity of 2.5 million lb. A new feature is that the cylinders connect directly to the riser string. The system costs significantly less, and weighs some 300 tons lighter, than conventional wireline riser tensioner systems, says Meling.

The knuckle-boom crane, an idea originally developed in the fishing industry, has its boom in two sections with an articulated joint. Hydralift's knuckle-boom crane, specifically designed with riser handling in mind, can handle risers weighing up to 35 tons at lengths up to 80 ft.

The addition of a lifting yoke also enables the crane to move tubulars in a stable fashion. Because there is no wire with a riser joint dangling from it, the pendulum effect experienced with conventional cranes is eliminated. Only one man is required for moving the riser sections to and from the catwalk machine.

Pipe-handling operations on the pipe deck are also simplified on the Stena Tay. Sections of drill pipe are easily lifted and fed into the pipe loader by a smaller knuckle-boom crane. These are then ready to be raised into the vertical position and assembled in three-section lengths.

The knuckle-boom crane provides a great flexibility and safe load-handling compared with other types of handling systems typically used for these operations, Meling says.

The HydraLift Rig layout also has the advantage of leaving three sides around the drill floor open, thus facilitating the movement of equipment to and from the drill floor.

The overall weight of the Hydralift topside equipment is significantly less than conventional equivalents. This means that the center of gravity of the rig is lowered, with beneficial effects on its motions, while the variable deck load is increased.

Orders flow

Hydralift currently has an order backlog in excess of NKr 1 billion. This positions the company as one of the world's major suppliers of deep-water drilling equipment, says Meling.

Combination large knuckle-boom cranes are also to be supplied to Transocean Discoverer Enterprise, Discoverer Spirit, Discoverer Enterprise III and West Navion II. All these vessels, plus Reading & Bates RBS-6, have also ordered the Hydralift N-Line Riser Tensioner System.

In addition, Hydralift will supply comprehensive drilling equipment packages to Ocean Rig, of which it is a part owner, for four Bingo 9000 hulls under construction in China. It will also deliver several BOP handling systems, cranes and other drilling related equipment to US based contractors.

Other customers include Saga Petroleum, which has exercised an option worth NKr 40 million for a riser tensioner system for the production risers on the Snorre tension-leg platform, while Shell Offshore in New Orleans placed an NKr 100 million order last year for the same type of equipment for its Ursa TLP in the Gulf of Mexico.

The company's expertise in drilling rigs and related technology incorporates the crane expertise it has accumulated over more than 20 years. It is the world's largest manufacturer of pedestal cranes and has delivered more than 200 cranes of various types to the offshore and marine sectors worldwide.