Expanding horizons
  from: Offshore Engineer
  by: Jennifer Pallanich
  Thursday, October 02, 2008

Designing the well with the completion in mind helps the operator to reach TD with a reasonable ID in the wellbore. US editor Jennifer Pallanich opens this month’s review of drilling and completion advancements with a look at how well planners have become increasingly reliant on expandable technology to help them achieve the desired wellbore diameter at TD.

Expandable technology helps drillers reach a targeted TD with the desired ID even if they run into trouble zones that ordinarily would have forced a decrease in wellbore size.

‘Anything we do is focused on getting the well to total depth with a large enough hole size by minimizing or eliminating the well’s telescoping effect,’ says Pat York, Weatherford’s director of commercialization and marketing.

More operators are opting to use expandable technology as a planned installation or planned contingency for getting through or past trouble zones. From a completions standpoint, using expandables makes a lot of sense.

‘You end up with an optimal-sized completion, and that’s what we mean when we’re talking about working with our customers to get more juice out of the ground,’ York says.

The allure of drilling smaller wells is also clear: economics, fewer bit sizes required and downsized and standardized equipment. ‘That was the vision that drew so many people into the monobore concept,’ York says, adding a caveat: ‘Solid expandables are not a panacea. It doesn’t fix everything.’

But what it does do is yield a larger hole size despite drilling or completion operations encountering trouble, he notes, and Weatherford has been working on the expandable reservoir completion technologies since 1995 and solid expandable technology since 2000.

‘You don’t need to have monobore or wells with a constant hole size drilled to the center of the earth,’ York says. The expandables should be selectively used where needed to obtain the optimal hole size for the desired completion, he says. Weatherford refers to multiple instances of single ID expansions as a monobore well and a wellbore with single instance of the technology as a monobore shoe extension or monobore open hole liner, as the case may be.

Part of what makes the technology work is combining an oversized shoe with a monobore open hole liner. For instance, an oversized tieback shoe on the conventional 13 3/8in casing with an expandable 11 3/4in x 13 3/8in monobore open hole liner will allow a deeper wellbore with the same ID as the conventional 13 3/8in casing. The tieback shoe for the 11 3/4in x 13 3/8in monobore openhole liner system consists a few joints of conventional casing, either 14 1/2in or 15in OD conventional casing. These conventional casing joints are run on the bottom of the 13 3/8in casing string and have sufficient ID to allow the top of the monobore liner to be fully expanded within them, resulting in an drift ID of the conventional 13 3/8in casing.

The liner running sequence for Weatherford’s monobore expansion with the oversized shoe entails eight steps: install the base casing with the oversized shoe; drillout shoe and underream the hole section; run the monobore shoe extension system in the hole; assemble the cone; pump cement; expand the monobore shoe extension system; expand the liner hanger; and drillout shoe.

Because of the use of the oversized shoe in the system, the monobore expansion must be planned as a contingency during the wellbore planning stage rather than hoping the trouble zone will not require casing off, York notes.

‘It’s all about preparing for troubles ahead of time,’ York says.

Customers who could extend the 133/8in well segment not just one time but twice or thrice ‘could drill almost any well in the world,’ York says. As such, he notes, the company doesn’t ‘have a zillion sizes,’ but Weatherford believes its offering contains the right combination of types and sizes to address the majority of customer needs.

Weatherford supplies the conventional expandable open-hole liner to extend 7in and 9 5/8in casing shoes. It supplies the monobore expandable open-hole liner to only extend the 13 3/8in casing shoe, although there are plans to add other sizes based on customer need. In 1Q 2009, Weatherford said it will commercialize a monobore open-hole clad liner that will allow the mitigating of trouble zones in an 8 1/2in wellbore without loss of hole size.

The biggest challenge has been overcoming the post-expansion collapse rating of solid expandable liners. Weatherford collaborated with BP during the development of the 13 3/8 monobore development to meet that challenge.

When expansion is done with a cone, York says, pipe ‘shrinks’ during expansion about 5% downhole. ‘The gain in girth of the expanding liner comes from somewhere; it’s not magic. It either comes “shrinking” in length of the pipe or a reduction in the pipe’s wall thickness, depending on circumstance.’

Either way, the expanded expandable liner winds up with a reduced collapse rating. A thicker pipe can be used as expanding thicker wall casing results in a higher collapse rating, York notes. The challenge is to not drive up expansion pressure required to expand the thicker wall casing, he says. To address this challenge,Weatherford uses a unique expansion method as well as a reduced casing yield.Weatherford uses 0.582in wall thickness on its 13 3/8in liner and 50ksi yield strength casing to expand rather than the 80ksi used elsewhere in the industry.

Lev Ring,Weatherford’s director of solid expandable technology, explains: ‘Two casings that have a diameter-to-wall thickness ratio of 20 (11 3/4in with 0.582in wall), and are expanded, say between 12% and 20% with one having a 50ksi tensile strength and the other having a 80ksi tensile strength will have only a 100psi difference in collapse strength after expansion.’ He says what drives this phenomenon is the fact that at high d/t ratio – where d is the diameter of the casing and t is the thickness of the casing – collapse strength almost does not depend on casing yield. ‘This means that the lower 50ksi steel can be utilized for certain expandable products without the detriment of significantly reducing its post expansion properties.’ The phenomenon can be taken advantage of to allow the lowering of the expansion pressure, lowering the system’s operational risks when the 50ksi expandable casing is used, he adds.

Weatherford’s engineers are also working in other areas to minimize operational risks of running expandables; one of these is by using collapsing cones, York says. During a ‘bottom-up’ expansion of a liner, if operation cannot continue, the non-collapsible expansion cone, which historically has been solid and manufactured of hard tool steel, could not be retrieved from the wellbore. Weatherford’s expandable cone can be collapsed, allowing the retrieval of the expansion tools through unexpanded pipe and preventing the need to sidetrack.

Blue dreams

Key in developing any new technology is collaboration with customers, notes Tom Tilton, group vice president of research and engineering: ‘We haven’t tried to just do it on our own, so I think that has given us a high success rate.’

Collaborating with a client on new technology can halve the design time needed from concept to field trial, he says. Central to that speed, Tilton adds, is that Weatherford is designing exactly what the customer wants, rather than what it thinks its customers may want.

In short, he says, clients want to understand and minimize risk and collaborations allow just that. Ring, whose engineering work in expandables dates back to the original R&D team at Shell, says Weatherford’s strategy of incrementally evolving technology and commercializing it actually speeds development time. He said the company has found that by breaking blue sky technical projects into intermediate deliverables with products that can be commercialized as the development progresses gets the company to its goal much faster than other development strategies.

Solid expandables hold a secure place in the drilling industry’s history with patents back to 1865, before wellbore cement was invented.

In the late 1990s, solid expandables started seeing successes in the offshore arena when the first expandable open hole liner was installed in the Gulf of Mexico, but a monobore well was out of reach at that time. The turning point in monobore technology came when individual technologies caught up with the dream of preserving hole size, Tilton says.

‘Over the 10 years, (the industry has) developed the building blocks required to actually develop this,’ Ring adds. ‘The idea is so beautiful and so big.’

Four or five years ago, York would not have expected the level of demand for the monobore technology to extend the 13 3/8in casing shoe because it was thought that any monobore efforts would need to be associated with extending the 9 5/8in casing shoe or smaller, especially given the status of the 8 1/2in hole as the most drilled size.

‘After doing a lot of research into well designs globally, I have found that if we can give our customers a 13 3/8in string with no loss of hole size, that’s a big deal,’ York says.

With over a thousand instances of solid expandables in the ground now, the technology has gained acceptance across the industry; however, the installations often stemmed from a lack of options. ‘The uptake of this monobore shoe extension has been very significant,’ York says. ‘Now the equipment is getting out there and being used.’

Customers have begun planning the monobore technology as a contingency against hitting trouble like rubble zones and having to lose hole size, he says.

‘People went from “Oh my god, I’m gonna lose the hole section or the well, come help me” to let’s use this as a planned installation or planned contingency and downsize our wells,’ York says.

There’s demand for the technology in both the deepwater GoM and Caspian as well as interest in the North Sea and offshore North and West Africa. York says the system is being designed into several well plans in these regions.

In 2007,Weatherford figured out the elusive answers to challenges associated with repeatability of monobore technology in a single casing size and filed for multiple additional monobore patents that covered their latest thinking.Weatherford believes it will be able to drill the first monobore well offshore based on that technology in 2011.

In 2008 offshore Saudi Arabia, Weatherford took six hours to expand 2175ft of 5 1/2in casing and introduce seals along the casing to isolate five zones. One goal was to prevent the galvanic activity associated with aquifer water contributing to the ‘rotting’ of the casing.Weatherford applied an expoxy fusion coating to block the galvanic action and prevent corrosion of the expanded cased hole liner.

‘Cased hole remediation is typically within tight economic constraints, therefore we didn’t want to go out and create expensive, complex cased-hole expansion equipment,’ York says. The service company opted to beef up their existing HOMCO expansion running tools, which has been expanding corrugated casing liners since the 1960s, for their cased-hole liner systems. This is the expandable equipment that was used for the Saudi Arabia work.Weatherford spent about a year developing the expandable casing with protective epoxy coating at the customer’s request.

In another well, this time with BP in the on the Shah Deniz Alpha platform in the Caspian Sea, using a 5 1/2in chrome expandable cased hole liner, a casing leak was repaired in a prolific gas well. The customer needed to return the well to production as soon as possible after trying other means of remediating the leak without success. The specially designed chrome patch was designed, tested for the gas tight 9000+psi application and installed within a three-month window, York says. The installed liner has been in place over the past year, and the well’s pressure and temperature has varied greatly without any performance derogation, he adds.

‘It’s all about the completion,’ York says. ‘If we can get the completion right, the economics of the well can work out.’OE

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