DRILLING & PRODUCTION

William Furlow
Houston

• Shown is the modular advanced tie-in system (MATIS)on trial at Shell UK Expro's Mallard development, claimed to be the world's first diverless flange assembly system. On Mallard, it was deployed to tie in two 8-in., 1,500-lb rated flanges. Designed by Stolt Comex Seaway and Hydra-Tight, MATIS conists of a carousel pre-loaded with stud bolts and a bolt tensioning system. It can operate in depths down to 1,500 meters on any diameter pipe, with rigid or flexible spools. [18,877 bytes]
• The 6-in. prototype of RigiFlex serrated pipe was recently tested on a bend test stand while a strain gauge recorder kept a record of its performance. [15,686 bytes]

Rowan using dual mud systems to combat synthetics loss

Rowan's new Super Gorilla jackup, now being fabricated in Vicksburg, Mississippi, will feature dual mud systems, one of the latest developments that allow drillers more flexibility when formations fracture and drilling fluid starts flowing.

The full system consists of six pits, each with a capacity of 5,200 bbl. The mud pump suction, mud mixing suction piping, and valves allow the two systems to run independently. This means the vessel can carry two types of mixed drilling fluids, presumably one tank of high-cost synthetic mud, and one tank of less expensive water-based mud.

This allows for an easy and quick switch to water-based mud if a fracture in the formation begins to take synthetic fluid from the borehole at a $800/bbl clip. Another nod to the importance of conserving this high-priced good is a slanted bottom on the tanks that allows the pumps to get every drop. When one considers it would be cheaper to pump French champagne down the borehole than many of the new muds, it is easy to see why this would be a popular feature on a newbuild.

Rigiflex offers a new twist

ABB Vetco Gray is developing a serrated steel flowline that could serve as an alternative to flexible pipe in the short jumper market, and possibly other applications. The product is called RigiFlex, a design based on the same principles as the Slinky steel coil (rigid when collapsed and flexible when extended).

The steel outer carrier pipe is scored with a series of shallow slits. The inner casing is made of stainless steel and is corrugated. The two bodies work together to provide the pipe with a high bending moment.

"The bending moment is slightly higher or near the range of existing lines," said project engineer Ralph Ruesse. Ruesse said he has built and tested two prototypes and is ready to move on to the next stage of development. RigiFlex is made of metal, with the exception of the wrappings, sleeves, and isolation materials. This provides an advantage in two well types:

•High temperature/high pressure wells (HT/HP): Using a metal flow line means a system can have metal-to-metal seals between the wellhead, christmas tree, and flowline. This is necessary in subsea HT/HP completions, where temperatures exceed 400 degrees F and pressures range up to 15,000 psi.

•High gas content: Natural gas can penetrate the elastimer materials used in synthetic flexible joints, escaping from the inner tube. However, gas will not penetrate stainless steel.

Because the tubing is made of line pipe with a special inner sleeve, it will be produced in standard 40-ft joints that can be welded together to make required sizes. This reportedly shortens the delivery time and provides flexibility, since the joints can be welded in the field. Ruesse says the joints can be delivered almost as quickly as line pipe.

Current limits on production of the new pipe design are being imposed by machinery used to fabricate the prototypes. Ruesse said he has built and tested two joints of RigiFlex. He has tested a 5-in. prototype to 5,000 lb, and a 6-in. version which was successfully tested to 6,000 lb. He hopes to build a new machine that can handle longer sections of riser. Currently, the machinery is limited to 20-30 in. long sections. The plan calls for bringing a machiner online that can handle 20-ft sections by mid-1998, with the ultimate goal of a full 40 ft capacity. Ruesse said he plans to have RigiFlex on a rig by the end of 1998. In fact, he said he could produce a riser for commercial use by the end of the summer if he had a client to provide the specifications.

Ruesse said the cost of RigiFlex will be competitive with currently existing products, but should offer faster delivery because of simplicity in design and fabrication. The initial market for RigiFlex, according to Ruesse, will be in the North Sea, where the all-steel product could flourish with abundant HT/HP fields.

Race to develop 10,000-ft water depth equipment continues

More and more tools are emerging from the design boards and machining halls to deal with the seafloor forces in ultra-deepwater drilling. The latest is Cameron, which has developed a drilling and completion collet connector to attach the blowout preventer stack to the wellhead, especially for dynamically positioned vessels.

The connector is designed for 10,000 ft depths and for a combined loading of 5.5 million ft-lb bending, 3.0 million lb external tension, 300,000 ft-lb torque, and 15,000 psi internal pressures. Cameron says it will add a dual hub wellhead profile, while will allow connection of a standard Cameron HC connector in lower range loading situations.

Copyright 1997 Oil & Gas Journal. All Rights Reserved.