DRILLING RIG TECHNOLOGY SEMISUBMERSIBLE DESIGNS: Crazy Horse project to employ world's largest semisubmersible

GVA Consultants has won the award to design the combined production and drilling semisubmersible unit for BP's Crazy Horse Field in the Gulf of Mexico. GVA Consultants won the design contract for the hull, drilling system, mooring system, and accommodation facilities.

Jul 1st, 2001
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Artist impression of the Crazy Horse semisubmersible drilling/production system being designed by GVA Consultants.
Click here to enlarge image

GVA Consultants has won the award to design the combined production and drilling semisubmersible unit for BP's Crazy Horse Field in the Gulf of Mexico. GVA Consultants won the design contract for the hull, drilling system, mooring system, and accommodation facilities. Front-end engineering design is underway. Topsides processing modules will be designed by Mustang Engineering and built by J. Ray McDermott, while the hull will likely be built in the Far East.

The GVA 40,000 design unit for Crazy Horse unit will be the world's largest such structure built to date with a deckload of approximately 40,000 tons and a 130,000-ton displacement. Production design requirements call for 250,000 b/d of oil production along with 250 MMcf/d of natural gas in 6,500 ft water depths. It will be connected to the seabed by 20 high pressure steel catenary risers.

Since the semisubmersible unit will be built as a combined production/drilling unit, it will drill and service wells from the same floating structure. The crew complement will total 160 people.

Major cost savings

The unit's dual capability will provide very large capital savings over the life of the field. No additional rig will need to come to the location to intervene when wells need attention. This means that the unit will have good flow assurance without any production downtime.

Intervention can be executed more quickly because equipment will be immediately available. Scheduled maintenance will run more smoothly because it can be planned around routine supply boat runs, bringing needed intervention equipment and materials out to the field ahead of intervention operations.

Each well at Crazy Horse is expected to take six to nine months to drill and complete, so the cost savings for the initial field development will be significant. Though hiring of deepwater rigs is planned for the start of the drilling program, most development wells will be drilled by the unit.

GVA Consultants is examining the possibility of using a dual-derrick tower, one section for the major drilling efforts and a smaller one for pipe makeup and well intervention operations. This would increase the overall efficiency of the facility by having the smaller rig deal with routine pipe-handling duties. It also frees the main mast for heavier work. For well intervention, the smaller rig is less expensive to operate and it can handle the lighter duties of cleaning and treating wells when needed.

Safety features

The semisubmersible's four-column supports will stand on a ring pontoon, but the deck will be built differently from most systems designed for the Gulf of Mexico. Most facilities in this basin have a truss frame construction. The Crazy Horse production/drilling semisubmersible will have an integrated buoyant deck box as an added safety feature.

The integrated hull and deck create a robust design. High structural resistance and the buoyant deck box add residual stability. The large deck for the semisubmersible provides good segregation between the hazardous and non-hazardous areas. The facility will have six lifeboats, with double the capacity for the number of people onboard, and an MOB boat.

For more information, contact Robert Ludwigson, GVA Consultants: Tel: +46 31 10 67 70, Fax: +46 31 10 67 10, E-mail: robert.ludwigson@gvaconsultants.com .


Iranian-built semisubmersible to drill in the Caspian

GVA Consultants is leading a consortium of companies along with Sadra (Iran Marine Industrial Co.) of Iran to design and build a fifth generation semisubmersible rig for drilling in the Caspian Sea. The semisubmersible will have a 5,000 ton deckload, be capable of mooring in up to 1,000 meters water depth using an eight-point mooring system, and carry accommodations for 120 people. The owner, National Iranian Oil Company (NIOC), has embarked on building a unit to allow for drilling in the deepwater parts of the Caspian Sea.

The semisubmersible that GVA Consultants is designing and supervising to perform exploration drilling in the Caspian Sea is a GVA 4000 drilling unit. The semi will be built at Sadra's Neka yard in the southeastern corner of the Caspian. Sadra is the largest Iranian shipyard group with yards in both the Caspian Sea and the Persian Gulf. The company previously built a jackup drilling rig for the Caspian Sea.

NIOC has set an ambitious build-time of 32 months for the project with delivery targeted for Spring 2004. This timeframe is within GVA's earlier experience. The company, when it was a shipyard in the 1980s, designed and built a GVA 2000 semisubmersible in 15 months and a GVA 4000 vessel in 22 months.

The building of this new state-of-the-art semisubmersible will be done in three parts. Two sets of pontoons with columns will be built and launched. Next, the deck will be assembled and skidded out over the water onto jetties. Lastly, the deck will be lifted and the pontoon-column assemblies will be mated to the deck. The deck will have a weight of 8,000 tons.

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