ABS certification for Tarzan
ABS has awarded class certification for the Rowan Companies Inc.'s "Scooter Yeargain" jack-up-the first of four in a new series of Tarzan Class rigs targeted for shallow water and deep gas drilling.
The "Scooter Yeargain" has recently entered service, and ABS has begun the design review process for classing the "Bob Keller" jack-up, the second rig in the Tarzan series.
ABS completed its review of the "Scooter Yeargain"-classed as an XA1 Self-Elevating Drilling Unit-in less than one year.
This is "record time," says Bret Montaruli, ABS manager of Offshore Engineering. "We met the client's deadline by maintaining an unprecedented level of contact with the rig designers," said Montaruli.
Rowan's LeTourneau yard in Vicksburg, Miss., fabricated the "Scooter Yeargain" with thorough on-site support from ABS surveyors, says Montaruli.
LeTourneau will build the Rowan's remaining three Tarzan Class design jack-ups, specially designed to drill deep gas wells down to 40,000 feet in shallow water ranging from 15 feet up to 300 feet.
"We've developed an excellent relationship with LeTourneau over the years, handling a range of projects. We're eager to assist Rowan and LeTourneau in their Tarzan Class endeavor as it holds great promise for continued Gulf of Mexico development," says Montaruli.
The rapid review process is part of an overall ABS initiative to tailor its engineering services to better support fast-track projects, particularly in the offshore sector. ABS, says Montaruli, has developed and is in the initial stages of implementing new engineering software that facilitates the tracking of projects.
"This software gives us greater flexibility while improving response time to projects such as the new Tarzan design rigs," says Montaruli. He adds that the new program allows ABS to conduct the design evaluation and overall approval electronically, maintaining constant dialogue and complete transparency with the owner and yard.
The Tarzan Class design is a lighter-weight version of Rowan's "Gorilla Class" and "Super Gorilla Class" designs, with the hull half the size of the Gorillas, explains Linda Hansen, ABS technical coordinator. Both designs originated from Rowan subsidiary LeTourneau.
The Rowan "Gorilla Class" and "Super Gorilla Class" design units, with their long-legged, high-powered specifications, are intended to drill in deepwater harsh environments. Both are capable of drilling deep gas wells down to 30,000 feet to 40,000 feet-about 15,000 feet deeper than the industry's aging jack-up fleet.
"LeTourneau took the powerful components used on the Gorilla and Super Gorilla Class rig and installed them on a vessel half its size," said Hansen. Hull weight of the "Scooter Yeargain" is 12,551.32 kips (1 kip equates to 1,000 pounds). The "Gorilla IV"the last unit of the original Gorilla Class-weighs 19,965.6 kips and the "Bob Palmer"the last unit of the Super Gorilla designweighs 21,129.86 kips.
The "Scooter Yeargain" dimensions are approximately 215 feet in length; 196 feet in width and 22 feet in depth, compared to the "Bob Palmer," which is approximately 306 feet in length; 300 feet in width and 36 feet in depth. Leg lengths on the "Scooter Yeargain" are 411 feet and 445 feet; "Gorilla IV" leg lengths are 504 feet and 605 feet; and "Bob Palmer" leg lengths are 578 feet and 712 feet.
ABS principal engineer Joseph Rousseau notes that the Tarzan Class design incorporates a rack-and-pinion jacking system rather than a triangular system, contributing to the lighter weight of the rig. He says that the "Scooter Yeargain" can jack up with up to 50 percent "preload"or water used to make sure the legs are embedded through soft mud and onto solid ground for rig stabilitywhile gaining more leg-length and increasing variable load, making jacking operations more efficient because less time is consumed emptying and filling the tanks. "That means the driller can set up on location faster and start drilling earlier. And drilling is what it is all about," said Rousseau. Most rigs, explains Rousseau, have to elevate then fill their preload tanks to push the legs into the dirt, and then empty the preload tanks because the jacking gear is not strong enough to lift the rig with all that extra weight of water. Although rigs with this design can hold position while embedded, they cannot lift; they have to elevate some more, refill the preload tanks to stabilize the unit, empty the preload tanks, and then repeat this process until they are firmly settled on solid ground. "A rig's jacking system is critical to safe operation at sea, as it elevates and supports the entire rig load. 'Scooter Yeargain' meets the design criteria for safety, using effective rack-and-pinion locking system," said Hansen.
The rig has a jacking capacity to safely lift 21,600 kips without preload and 28,350 kips with preload. Each leg is designed with 18 pinions capable of supporting 7,200 kips. "The 'Scooter Yeargain' is designed to rise up as much as 88 feet above the surface of the water, providing a clear, stable platform from which to drill," said Hansen.
The Tarzan Class design is equipped with five Caterpillar engines, model 3516B HD, capable of delivering a total output of 10,750-horsepower, considerably more than the Gorilla design, which is rated at 7,950-horsepower. The Super Gorilla design is rated at 16,975-horsepower. This increased power is necessary to drive the three mud pumpsthe industry's largest with each at 3,000-horsepowerand to handle the long strings of pipe 40,000 feet long required for the greater drilling depths. "Rowan has packed a lot of power into its new Tarzan Class design, making it sufficiently robust to take on deep-gas drilling," said Hansen. The LeTourneau yard is currently fabricating the "Bob Keller" jack-up, which is expected to be ready for work in September 2005. Construction of the third Tarzan Class unit should begin as the second one leaves the yard, with all four deliveries scheduled to complete by 2008.
In addition to classing "Scooter Yeargain," ABS acted on behalf of the U.S. Coast Guard, ensuring that all regulations are met and that the unit complies with the latest standards of safety environment. In terms of personnel safety, ABS reviewed both passive and active fire protection, in addition to the jacking system. Addressing environmental safety, ABS applied Marine Pollution Prevention (Marpol) standards, Annex I, IV, V and VI, which reflect the Shipboard Oil Pollution Emergency Plan (SOPEC), including sewage, garbage and air pollution. Founded in 1862, ABS is a leading international classification society devoted to promoting the security of life, property and the marine environment through the development and verification of standards for the design, construction and operational maintenance of marine-related facilities.
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