Newest rig features large pipe makeup- breakout area

Sedco Express utilizes pontoon storage, dual mud systems

William Furlow
Technology Editor

The Sedco Express fifth-generation semisubmersible is designed to lower turnaround times, and thus save money [27,356 bytes].

The Sedco Express fifth-generation semisubmersible offers a package of innovations that may point the way for the next generation of deepwater newbuilds. Olle Lorehn, Sedco Forex international marketing manager for North America, said the innovation in these newbuilds is more a matter of applying existing technology in new ways.

The Sedco Forex vessel design team, Lorehn said, included the usual industry and client input, but also individuals who had no experience in the business. Lorehn said these novices were courted not for what they knew, but for what they didn't know. "We wanted a completely new approach," he said.

Those with industry experience might have ideas that were more practical, but Lorehn said these advisors are hamstrung by their experience. They know what is practical, which means they may automatically dismiss some ideas that at first blush seem unrealistic.

Debottlenecking drilling

The primary goal of this team was to debottleneck the drilling process. Because of the rise in day rates in the Gulf of Mexico, where the new rigs would most likely operate, turnaround time can be a major cost. A common goal expressed by those looking into new designs is to hire a rig that can get the job done quickly and safely. This shortened turnaround time can mean substantial dollar savings.

Lorehn said the team identified the handling, making up, and breaking out of tubulars, as a real problem time-wise. Other priorities of this new design were increased safety, both physical and environmental. Lorehn said the team looked at ways to combine these goals into an integrated solution.

By surveying reported accidents on offshore rigs over the last decade, Lorehn said the team discovered the primary cause of the accidents was workers tripping and falling on the drillfloor. To overcome this danger, it was decided the new rig would have a larger flat pipe deck with pipe stacked no more than 6 ft high. Lorehn said the drill rig has also been heavily automated with six iron roughnecks.

Once the pipe is loaded on the vessel, it is mechanically handled throughout the operation. This modification also lends itself to efficiency. There are two iron roughneck stations set up on the deck, one to the port and one to the starboard. Each station has two iron roughnecks that can make up or break out pipe, casing, and riser strings. These strings are then set back in 125-130 ft stands to facilitate faster handling.

This solution eliminates the dangers involved in handling pipe manually, while making the drilling process more efficient. Two additional iron roughnecks are installed in the rig's expanded mast to handle pipe and casing.

With a time savings of several days for some drilling activities other areas of delay begin to stand out. For example, this time savings means the traditional mud systems, in which one pit mixes mud and then serves it to the pumps, would not be adequate. Lorehn said there would not be time for one system to mix and pump during the setting of the casing, because of the reduction in time required to run casing.

To overcome this problem, the Sedco Express has two mud systems that work in tandem, one mixing while the other pumps. The vessel can carry 4,600 bbl of mud on its surface pits and another 4,200 bbl reserve in each pontoon.

In addition to mud pits, the pontoons also contain a variety of other equipment including the engine room, mooring winches, mud pumps, and oil tanks. Lorehn said the pontoons were traditionally just filled with water, but as semis grew larger, they required larger pontoons with more room inside.

Eventually the option of filling these with something besides water became practical. This move cleared the decks, literally.

The pontoons are double hulled everywhere except in the areas designed to carry water. Also the columns are double hulled. Lorehn said the rear columns, which support the heavy mast and make-up stations, are larger than the forward columns to provide greater stability for the drill floor.

Newbuilds underway

There are two versions of the new vessel currently under construction. Lorehn said Texaco will receive the Sedco Energy in August of 1999. This vessel will be used in the Gulf of Mexico and includes an optional dynamic positioning system as well as the mooring system. Lorehn said the second vessel, being built for a contract with Elf, will not have the mooring system.

The D3 three-time redundancy dynamic positioning system which is the primary stationkeeping system on this new design, is engineered with the strong loop currents of the Gulf of Mexico in mind. The system is capable of holding the rig on station in a 3.5-knot loop current, with a 60-knot head wind in 26 ft significant seas. This is with one engine and one thruster out. Lorehn said these rigs are designed for moderate environments, such as the Gulf of Mexico and can be outfitted to drill in water up to 10,000 ft.

The mooring system features traction winches with over 1 million lbs of pull. The vessel can be conventionally moored in up to 2,000 ft of water or can grab onto a prelaid mooring system for a development or production project.

With the additional size and automation of these vessels the crews will be a bit larger. Lorehn estimates 50-60 people will be needed to run the dynamically positioned version. This new generation of roughnecks will very different from predecessors. These men and women will have to have field experience as well as the technical expertise needed to handle the increasingly complex systems.

Lorehn said the crew quarters on the new vessels have this next generation of worker in mind. Gone are the six-man bunk areas. They have been replaced by two-man suites with private showers. The crew quarters are constructed as a separate module; not only are they easier and less expensive to fabricate, but they do not transmit as much noise from the rig to the crew quarters.