Expandable solid casing reduces telescope effect

Aug. 1, 1998
A continuous cement lining can be applied to cure a trouble zone without sacrificing a casing string [62,496 bytes] Expandable casing goes into the well in one diameter, then as an expansion mandrel is either drawn through or pushed through, it expands by as much as 300%. The technology was recently developed and tested in a slotted form. This technology and a new solid form are the subject of several marketing alliances and offer a glimpse into the inner working of Shell's new technology

Shell device option on shallow flows

William Furlow
Technology Editor
Expandable casing goes into the well in one diameter, then as an expansion mandrel is either drawn through or pushed through, it expands by as much as 300%. The technology was recently developed and tested in a slotted form. This technology and a new solid form are the subject of several marketing alliances and offer a glimpse into the inner working of Shell's new technology commercialization company, Shell Technology Ventures Inc.

Shell Technology Ventures, incorporated several years ago, identifies additional value for technologies Shell has developed in research and development projects around the world. The idea is to get more mileage out of the company's research dollars by making technologies it developed commercially available faster, and capture some of the value created by selling these technologies to non-Shell companies. In the example of expandable casing, Shell has formed a joint venture with Halliburton Energy Services to develop and market the products and services in the US and is on the verge of signing a similar deal with Baker Hughes for applications outside the US.

Slotted expandable casing

There are two types of expandable casing, according to Tim Frank, Venture Development Manager for Shell. In the early 1990s slotted expandable casing was developed. By cutting vertical slits in casing strings, Shell was able to expand the diameter of these tubulars by as much as 300%.

Slotted expandable casing can be used as an alternative borehole lining. If a driller has a problem in an open hole zone while drilling, the slotted casing can be used to create a cemented-off section in that open bore. In such a situation, the slotted casing would be run, then cemented. Before the cement has time to set, the casing would be expanded. The result is a steel reinforced concrete barrier that can keep the drilling program on track.

Often, when a driller encounters a fluid loss problem in open hole, a cement plug will be set to seal off the zone, then an attempt made to drill through it. This works, but it is easy for the bit to wander off-center cutting through this plug. With the steel reinforcement, it is much easier to keep the program on track, while eliminating the fluid loss problems.

"The slotted tube acts as a reinforcement to the cement and a guide to take your bit right back to center," Frank said.

The slotted casing also has applications in horizontal well completions. Often the long, open-hole sections are completed with a perforated or slotted pipe that has an annular space around it. The slotted casing can be substituted in these instances to provide greater hole stability. Once expanded, the casing would eliminate the annular space, making it easier to perform remedial treatments. Because the casing maintains the full internal diameter (ID) of the open hole, it is easier to optimize this hole size.

In addition to applications in open hole, Frank said the slotted casing and cement option can be applied to a trouble zone with a smaller conductor string.

Frank gave the example of a well that starts out with a 20-in. conductor casing. The driller would run a 13 3/8-in. liner through the trouble zone, then follow this with a 9 5/8-in. casing string so he can end up with a 7-in. production conduit. With slotted expandable casing, a driller could start with 13 3/8-in. casing, use slotted tube and cement through the troubled zone, drill through that, and set the 9 5/8-in. and 7-in. strings. This design gives the same production conduit without sacrificing a casing string to overcome the trouble zone, allowing the driller to use a much smaller initial casing string size.

Solid pipe expansion

Currently, solid expandable casing has only been expandable to 30%. The goal of this technology is to develop a uniform casing size that can be expanded downhole, reducing the telescoping effect that limits current casing programs in ultra-deepwater.

In deepwater fields, a traditional casing program may result in a production conduit that is too small to produce a reservoir economically. With common problems found in the deepwater areas of the Gulf of Mexico, such as shallow water flow zones, casing sizes can drop quickly as drilling progresses, leaving an operator with no alternative but to plug and abandon.

Even in viable fields, where total depth can be reached with a producible annulus, there is still a weight consideration. Richie Pickins, Vice-President of Marketing for Shell Technology Ventures, said this slimhole design will have some major impact for drilling in ultra-deepwater fields where increased deckloads and hookloads force the construction of larger and larger vessels.

The solid expandable casing design addresses both of these concerns. It can be run in a tighter program, expanding as each string is set, so that the same bottomhole annulus is achieved with a conductor casing that is nearly half the diameter of a conventional conductor string. In addition, shallow water flow (SWF) or other trouble zones can be sealed off without sacrificing a casing string. The casing run through the troubled zone is expanded to the same size as the string it is hung from, so that the zone is sealed off and drilling can continue without the loss of a casing string.

The solid expandable casing also has applications as a casing patch. Once it is expanded into a damaged area to repair or patch the original casing string, there is minimal loss of hole ID. This casing also could be used as a drill liner or a contingency casing with minimal loss of hole ID. In fact, according to Frank, under-reaming can all but eliminate the reduction in ID caused by the expandable casing.

Rather than reducing the integrity of casing, the expansion process actually "work hardens" the metal so that it is as strong or stronger in the expansion mode as it was originally.

The advantage of solid expandable casing, compared with the slotted product, is that the pressure containment is not reliant on cement. Also, eventually, as the technology advances, it will be possible to construct a well using this solid expandable casing. This well construction would maintain the same bottom hole ID with a much slimmer well profile.

Frank said the casing can provide a method for patching casing and sealing off troubled zones without impacting the hole ID. Frank estimates the well profile would be reduced by around 50%, cutting costs significantly.

The slotted expandable casing is being used in the field currently on a limited basis and has completed some commercial runs, but none yet offshore.

The solid tube expandable casing is not yet commercialized, which is the reason behind the Halliburton and pending Baker Hughes joint ventures. Casing patch tests with the solid expandable casing will be conducted later this year. Frank said he would like to see these technologies applied in the Gulf of Mexico and North Sea by the end of 1999.

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