December 2004 Supplement    New Rig Designs

Ultra-harsh environment jackups

Maersk Contractors’, of Copenhagen, latest Ultra-Harsh environment jackup rigs, the Maersk Innovator and Maersk Inspirer, are set apart from other rigs due to water depth capability, efficiency and variable deck load. Deeper water, higher deck loads and improved efficiency, combined with higher environmental standards were drivers behind the new design, which Maersk developed in cooperation with Marine Structure Consultants. The Innovator, delivered in January 2003, was working for Total in Norway in late 2004, then started a four-year contract with ConocoPhillips in Norway. Inspirer, with basically the same design, was to arrive in the North Sea from Hyundai Heavy Industries in Korea by year-end 2004.

Maersk Innovator jackup working on Total’s DP2 platform in the Norwegian North Sea.

With a 205-m leg length, Innovator is capable of operating in most harsh environments at water depths up to 150 m. In less demanding areas, like the Gulf of Mexico, this design can work year-round in water depths to 190 m. The spudcans, covering an area of 400 m² each, are fitted with 2.5-m skirts. On most soil conditions, a skirt will increase seabed moment capacity and thus increase ability to meet higher environmental loads. Moving the jackup boundary in respect of water depth, combined with subsea capability, enables the new rigs to cover more than 80% of the existing subsea installations in the UK sector and 40% in the Norwegian sector.

An important design element is use of a high-capacity leg fixation system that permits operation with a variable load of 10,000 metric ton, mt. Available deck space of 2,500 m² is more than twice that of a traditional harsh environment rig. All mud treatment is built into the cantilever, and the cantilever bottom is raised 3.5 m from the main deck. The longer cantilever makes it possible to place arriving tubulars directly on the cantilever deck.

Relocating the 120-person accommodation makes it possible to create a large deck area, minimizing deck-to-deck crane activity and introducing use of a deck forklift. And the new cantilever type on Innovator can skid transversely as well as longitudinally as one fixed unit, thus avoiding need for a transverse skidding substructure for the drill floor.

The drilling envelope has been increased significantly. Cantilever distance from stern to well center is 27.4 m, and maximum transverse skidding distance in 19.8 m. This, combined with the 205-m (plus optional 40 m) leg length allows the rig to reach most wells on platform installations. Combined load capacity is 1,400 mt in all areas of the drilling envelope at 89-ft reach, and beyond that, 900 mt, allowing non-restricted skidding.

Dual pipe handling has been introduced in the drilling process, reducing non-productive time as well, as a dual drilling fluid system. Coiled tubing or wireline operations can be carried out in parallel with other drilling operations.

The 75-m derrick allows for drill pipe to be racked in stands of four joints, enabling drilling with 41-m stands, compared with the usual 29 m, as well as being able to rack three-joint stands of casing, reducing casing running time by up to 60%. In total, 9.2 km of drill pipe and 5.5 km of casing can be racked in Innovator’s derrick at the same time.