December 2004 Supplement    New rig designs

New jackup design supports ultra-deep drilling trend

As oil and gas exploration has evolved, industry has turned to ultra-deep drilling in its search for new reserves. To meet the need for efficient shallow-water, deep-drilling activities, the Marine Group of LeTourneau, Inc., developed its new Tarzan Class jackup. The new rig is designed for year-round operation in water depths of 150 to 250 ft, and drilling depths to 40,000 ft. An entirely new class of jackup, the rig combines the latest design technology with the company’s proven track record, representing a natural extension of its industry-leading, almost 50-year jackup history.

The result meets evolving needs brought about by more complex drilling operations, industry innovations, and more stringent safety and environmental requirements. The new design is unique in that it provides for highly efficient, ultra-deep water drilling. It was specifically engineered to survive a range of severe storm conditions up to 71-ft seas and 100-kt winds in 150-ft water, or 55-ft seas and 100-kt winds in 250-ft of water. It utilizes LeTourneau’s opposed-pinion elevating system, a triangular-shaped hull; and it is equipped with three open-truss legs of triangular cross-section. This design has resulted in a significant increase in the environmental criteria and load carrying capacity under both drilling and storm conditions.

The rig’s hull is equipped with engine/ generator systems, marine and drilling mud processing equipment and storage rooms, an accommodation superstructure for 82 people, a helideck for use of an S-92 helicopter, and a cantilevered drilling assembly.

Utilizing the new LeTourneau 440-kip elevating unit, the rig is a tested and proven evolution of the prior units and a 7,600 output pinion history. The simple and effective leg guide and pinion system provides a stiff leg-hull interface during all phases of operations. And, because the leg design employs the company’s tubular cross-section chord configuration, it results in reduced drag/ storm loading, and high strength and stiffness-to-weight ratios.

Providing up to 2,500 kips drilling load capacity and full 50-ft reach, the cantilever and substructure skidding features an 800-kip pipe rack and 1,000-kip setback loads. In addition, the design provides six active mud pits and two slugging pits with a 2,200-bbl combined capacity. The mud system accommodates oil-based and water-based muds simultaneously, while maintaining zero pollution provisions, including all wastewater collection and treatment.

Built on contract for Rowan Companies, Inc., the premier Tarzan Class rig was christened the Scooter Yeargain on April 3, 2004. The rig’s first assignment was for Anadarko Petroleum Corp., in the Gulf of Mexico. It is presently completing a project for Millenium Oil and Gas Co. in the US Gulf. In addition to the new jackup, LeTourneau has designed and built 179 jackups, including the 82SD-C, 116-C, Super 116, Super 300, Gorilla, and Super Gorilla XL designs, comprising the company’s remaining 56 other jackups now operating in the Gulf of Mexico. 

Scooter Yeargain shallow-water, deep-drilling jackup operating in the Gulf of Mexico.