Multiple-conveyance capability garners support for expandable patch
Chris Nussbaum, READ Well Services, Aberdeen
Small to medium-sized enterprises with lots of intellectual property now typify the sorts of companies bringing new ideas
to the North Sea and elsewhere. Aberdeen-based READ Well Services is one such company, and has taken a different approach in developing its Hydraulically Expanded Tubular
System (HETS), using hydraulic pressure directly inside a tubular to expand it. This process, known as autofrettage, is a relatively old and widely used industrial
process (e.g., re-lining gun barrels). The company has taken this process into the downhole well environment.
Due to the patented, high-pressure seal arrangement of the HETS tool, rated to take a differential pressure up to 30,000
psi, the pipe expansion process and the solutions provided are quite different from other tubing-expansion systems. The tool can expand two concentric casings
simultaneously – including high-strength steels up to P110 and heavy-wall casing. The inner casing is expanded into the outer casing and then the combined casings
expand to form a metal-to-metal interference fit.
Applying hydraulic pressure to achieve expansion in this manner ensures that the casing being expanded conforms precisely
to the surrounding shape, even if it is somewhat irregular, providing a good pressure seal.
Over the past three years, the company has introduced expandable products for well construction. The systems can be
deployed are on coiled tubing for live wells, on drill pipe, and this year will see the launch of a wireline-based deployment system. Much of this development work has
been, and continues to be, supported by Statoil, by providing funding and field trial opportunities that are so important in new technology development.
Field application. The first application developed was for an external casing patch, sometimes referred to as an
overshot casing patch, which is used to reconnect new casing to a casing stub downhole when the original casing has been cut – perhaps to remove a damaged section,
because of a leak, or because it has become stuck (see World Oil, July 2003).
The HETS tool is utilized to expand the casing into a profiled overshot, with the resulting connection capable of carrying
hundreds of tons of tension and compression. It can be tested to high burst-collapse ratings using metal-to-metal gas-tight seals only.
An external casing patch can be used for casing repair or as a slot recovery technology. A typical application for Statoil
on one of its HPHT fields is an overshot patch system on standby while running 14-in. P110 as a contingency in case of stuck casing; and the system is fully qualified to
500-t tension, 300-t compression loading and 440-bar gas pressure.
“Using the HETS external patch during Kristin field development provided us with an available and qualified
alternative to a costly sidetrack if casing became stuck,” comments Erling Mathiassen, staff engineer R&D Department – TAIL Production, with Statoil. The
gas-tight seal and the load-bearing capability of the HETS connection was extensively qualified during onshore tests.
“Statoil has made a commitment to this development,” Mathiassen adds, “because we see other uses for this
technology – the larger sizes offer an excellent method of casing replacement and repair for slot recovery.”
Another North Sea application involved a casing patch to tie back casing as part of a workover. Within the well, the
casing had been damaged when an annular safety valve was pulled. The damaged 103D4-in. casing was cut below a 9-5/8-in. crossover and a HETS EP system was tested. The
testing required both loads and burst-collapse testing up to 2,300-psi gas to meet specifications for gas lift in the annulus between the 9-5/8-in. and the 7-in.
The second development of the HETS expandable system, which was exclusively sponsored by Statoil, provides an expandable
solid tubular internal patch, up to 10 m (32.8 ft), that is run and expanded in place on coiled tubing or drill pipe to repair or reinforce tubulars downhole. Statoil has
a very large inventory of subsea wells and also many mature wells in the Norwegian sector.
“The internal patch system is essentially a well intervention or workover technology – to repair leaks, provide
protection of tubulars during thru-tubing rotary drilling, or to mechanically reinforce the corroded zones of a wellbore,” explains Mathiassen. “This system
gives us the option to repair wells, even subsea wells, instead of working them over. With rig rates so high, avoiding the cost and time of a complete workover is a
Internal casing patch, expanded using direct hydraulic pressure, deployable on CT, drill
pipe or wireline.
“The current version of the internal patch is designed for 7-in. monobore wells – and the fact that it can be
deployed into a live well on coiled tubing offers good operational flexibility for Statoil. This first tool was designed very much with the main well inventory in Norway
in mind, but the next generation of slimmer tools is already in design.”
Complex and challenging wells are now attracting attention from the company, ranging from HPHT applications on Statoil’s
Kristin field, to gas-lift wells and deep, extended reach wells.
Technology drivers. The future for autofrettage in the downhole environment is clear. The Aberdeen-based firm
believes that a major appeal for operators is the metal-to-metal seal, which is capable of carrying high loads in both tension and compression. Several operators in the
North Sea consider the technology viable and have actively supported the company and its technology. Five majors are now participating in HETS developments. However, the
industry is inherently conservative and uptake of new methods is inherently slow – there is always a long line to use new technology once someone else has deployed
it successfully for the first time.