Deepwater role seen for solid expandable tubular systems

The solid expandable tubular systems that Shell Exploration & Production Co. used to drill its Baja well in the Gulf of Mexico mark a major step toward slimhole drilling technology in deep waters.

Sam Fletcher
OGJ Online

HOUSTON, Apr. 30 -- The solid expandable tubular systems that Shell Exploration & Production Co. used to drill its Baja well in nearly 8,000 ft of water in Alaminos Canyon Block 557 in the Gulf of Mexico mark a giant step toward slimhole drilling technology in deep waters, said a company executive.

"I think we're certainly starting to see a slenderizing of our wells. The other option if we hadn't used this is to make everything bigger -- step up to a 18 3/4 or a 21-inch riser system," said Paul Goodfellow, floating rigs operations manager for Shell Exploration & Production in New Orleans.

At a Houston deepwater technology session sponsored by the Society of Petroleum Engineers earlier this month, Goodfellow said, "Ultimately where we are heading is to the mono-diameter well -- one size of pipe that you continuously run and drill with coiled-tubing. Once you've got to your depth, you basically expand that coil, cut it, run in and drill the next section, and expand it back into the previous one.

"On slender wells, the next step is really neck-to-neck expandables -- expanding inside of expanded pipe. Instead of going normal API pipe, expandable, normal API pipe, expandable, you double or triple up the expandables."

He said, "Going to the compact rig, using this technology with subsea pumping and the advance synthetic mooring systems that being developed, is not too far into the future."

Shell used R&B Falcon Inc.'s Deepwater Nautilus semisubmersible to install the expandable tubulars in the well in 7,790 ft of water (OGJ, Mar. 12, 2001, p. 48). The deepest anchor on that moored rig was in 8,250 ft of water, said Goodfellow.

"We're just about to bring out the next version of that, using a synthetic line rather than steel wire and chain. The whole thing starts to get smaller and more moveable, so that you don't need the number and size of supply boats with it," he said.

The Baja well proved the technology of solid expandable tubulars, said Goodfellow. "Without this, we would not have been able to drill to the primary objectives on this well," he said. "We actually put in three additional strings of casing, through the technology of expandables and big-bore wellhead, that we wouldn't have had in our armory if we hadn't gone through the development and testing cycles. If we had not done this, we would have run out of casing way, way before the primary objective."

That success "certainly provides a confidence to us that expandable technology and expandable tubulars can be applied on a much, much wider scale," he said.

As a result, he said, expandable drilling technology "is nothing magical to us anymore. It's really being planned on all the deepwater wells that we have where the margin is narrow. This is a safer way to get the well down.

"This is certainly one tool that you can use to overcome the low margin environments that we see in some parts of the deep water in the Gulf of Mexico and other areas of the world," said Goodfellow. "But it's just one example of expandable technology. A lot of us are looking at expandable sand screens to try to get away from having to pump large sand treatments on the wells. The key is the exchange of learning so that we don't have to reinvent the wheel."

Enventure Global Technology LLC, a joint venture between Shell Technology Ventures Inc. and Halliburton Energy Services, developed the unique solid expandables used in drilling the Baja well. No one else has anything like, said Shell officials.

"The basic principle of expansion is cold-working steel downhole," Goodfellow said. That means taking the metal "past its yield point into the plastic region, but not taking it so far that it fails." The metallurgy permits "generally up to about 20% expansion factor, with something like a 5% reduction in length."

However, he said, "The force that you need to expand that pipe is very, very low -- generally 5-10 tons of pull and 1,500-1,800 psi of pressure will get that pig moving." That's because the expansion tool is designed "so that the steel flows over it and you don't have a huge amount of friction force that you have to overcome."

Otherwise, the solid expandable tubing "looks just like any other casing," said Goodfellow. "It's run with the same tools. It's made up the same way. It's just a little bit of technology and metallurgy in the tools that are inside that shoe joint to allow you to expand it."

At present, expandable tubing costs about twice as much as conventional pipe, "purely because of the design and development work. But we can drive the cost down by using more of it," said Goodfellow. Still, even the higher cost "is well worth it," he claimed.

Shell engineers in The Hague did original research on solid expandables technology. By the time the company decided in 1997 to go forward in developing that technology, Goodfellow said, "We saw it as a moderate risk from a technical point of view. There had been some small scale and lab work done, but it really hadn't been developed into an application for day-to-day operations."

What Shell gave Enventure was "very much an idea. What we have done together is to take it to something that is a commercial, reliable application that certainly we consider a standard now on every well we look at in the Gulf of Mexico," Goodfellow said.

"One of the constraints was that we wanted to use traditional casing sizes -- not have to go out and design everything special from top to bottom. And we wanted to run conventional API-size pipe after setting the expandable casing," he said.

Therefore, Shell engineers drew up a portfolio of three types of wells in which they thought expandable casing would be most applicable. "The first was a 13 3/8 by 16-in. system that we could run a 13 3/8 pipe through after it had been expanded. The second in order of priority for us was a 9 5/8 by 11 3/4 system, again that we could run a standard 9 5/8-in. pipe through after it had been expanded. And the third was a 7 5/8 by 9 5/8, which we really saw as a contingency that we could utilize if we had problems once we got down to objective depth.

"It is probably more applicable to the subsalt environment as well. Once you get below the salt, you can have trouble with the rubble zones that tend to accumulate around the salt."

A key question addressed by the research team in the design phase was whether to expand casing from the top down or the bottom up. "Both have their pros and cons. We settled on bottom up -- not only is it easier to expand that way, but also it gives you a get-out if something goes wrong. You can cut that out and sidetrack around it. If you're coming from the top down, you can get yourself in a nasty position where you have to come way up the well or try to mill out an expanded bit of pipe," said Goodfellow.

Before Shell tried the new tool in deep water, he said, "We made a conscious decision to test this in two of our South Texas gas wells. That in itself can be a huge barrier to overcome because you have very much misaligned objectives."

The first test was successful, but with the second well, he said, "We learned that what actually happens sub-surface in the real world can be different from what you can model in the office."

Goodfellow said, "We had a successful expansion, but when we went back in to drill out, we found we had collapsed the pipe right at the base of the expanded section." Workers found that movement of the expansion pig through the pipe lifted a column of fluid, which sent a pressure wave back down to the bottom and collapsed the pipe.

The lesson, he said, is that "you really have to think about what happens not just during the expansion but after the expansion as well."

In a third test, the expandable pipe became stuck. "We expanded it up hole 82 ft and then lost pressure. What happened is that the pipe had parted," Goodfellow said.

"The fact that we tested in a low-cost environment was the key for us. The well in Alaminos Canyon cost enough. If we'd had to suffer some of the failures from these early trials, I believe we wouldn't have drilled the well down to TD," he said.

Through the Enventure joint venture, Shell took solid expandable tubulars from a concept to a commercial deepwater tool in just over 3 years. "I would have liked that to be faster. But looking at the work that was done, that was probably a realistic time span to take any technology from a drawing board stage to something in the engineer's toolbox for day-to-day use," said Goodfellow.

Contact Sam Fletcher at Samf@OGJonline.com

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