The expansion of concentric downhole tubulars with direct hydraulic pressure has been advanced by READ Well Services with the Hydraulically Expandable Tubular System (HETS).

Figure 1. The HETS expansion tool can retain pressures up to 30,000 psi between its two dynamic seal elements. (All figures courtesy of READ ASA)
Developing a completely new liner hanger design in just 14 months would be a challenge in its own right, but this project delivered a hanger-packer assembly that would prove able to withstand the rigors of 20 days in a drilling-with-casing environment and then be expanded and set with a load capability of over 200 tonnes and a 5,000 psi, gas-tight seal tested to ISO 14310:V0.

The well itself presented the operator with extreme challenges, even by the high standards of the North Sea. The twin-wellhead design required casing directional drilling to over 12,000 ft (3,660 m) measure depth with up to 70° deviation, and conversion of the 7 3/4-in. casing-drilling string to a liner, with an integral, completely gas-tight, 200-tonnes capacity liner hanger/packer assembly set at 5,000 ft (1,525 m) in the 10 3/4-in. parent casing.

Casing directional drilling
With the drill bit at a depth of approximately 7,000 ft (2,135 m) the HETS liner hanger was installed as part of the a casing directional drilling (CDD) string. The string then drilled ahead to the 7 3/4-in. shoe depth at 12,000 ft. The casing shoe was cemented, and the HETS expansion tool was then run into the well on drill pipe and engaged in the liner hanger using an integral latch device. The HETS system was activated, and by generating 21,500 psi hydraulic pressure (above hydrostatic), expanded the 11-ft (3.35-m) long hanger by 15% in diameter, thus successfully setting it in the 10 3/4-in. parent casing. The water-based hydraulic fluid for the expansion was carried in a reservoir compartment in the drill pipe immediately above the expansion tool.

Successful installation was confirmed by a 5,000-psi pressure test, after which the entire 5,000 ft casing string above the HETS liner hanger was retrieved from the well by activating a specially designed release mechanism.

Development partnership
The relationship between the service company and the operator is a good example of how to deliver technology though partnership between a small service company and a major multinational operating company. The service company was invited in late 2005 to present conceptual solutions to a number of challenges in the well construction program. Within just a few weeks of submission of the liner hanger concept, the operator had initiated a development project with the service company that would deliver a fully qualified liner hanger before the end of 2006. The ambitious project would also encompass the design and build of a downhole power pack for wireline deployment of the expansion tool.

The fast-track project required the design, building and testing of a series of six liner hangers, from prototype to final design. The extensive hanger test program set out to establish the load and sealing capability of the liner hanger as well as its ability to withstand a drilling-with-casing environment. The gas-sealing capability provided an essential barrier against gas migration potential in the well.

An ISO first
The tension/compression test-bed facility at the service company was used to subject the
Figure 2. The expandable HETS Liner Hanger design creates a slimmer connection, which has bi-directional load-bearing capability.
test pieces to loads up to 360 tonnes. Each test piece was a full-size hanger expanded and set in a 10 3/4-in. casing section. The liner hanger was tested in accordance with the ISO 14310 Packer Standard, which required the liner hanger to be cycled through both internal and external gas and hydraulic pressures of 5,500 psi across a range of temperatures from 15°C to 115°C (57.9°F to 237.9°F). A leak rate of zero (V0) was successfully established in the tests.

Subjecting a complete liner hanger and casing assembly to nearly one million bend cycles under pressure evaluated the mechanical durability of the hanger. The mechanical integrity and 5,500 psi seal rating of the hanger remained intact throughout.

Expandable liner hanger
The HETS expandable liner hanger is specifically suited to tight-clearance, liner-to casing-completions and DWC (drilling with casing) applications. Advantages include:
• Suitable for tight-clearance casing systems;
• No slips or moving parts;
• Metal-metal and elastomer seal combination;
• Bi-directional load capability;
• Standard grade liner to casing connections; and
• Custom sizes for flexible design.

The expandable liner hanger design creates a slimmer connection, which has bi-directional load-bearing capability. The hanger has synergies with an overall slim well philosophy and increases the options for contingency drilling liners. It has no moving parts (in particular, no slips) and a unique combination of metal-to-metal interference-fit and elastomer seals — simplicity that should result in lower failure rates than those of conventional hangers. The design lends itself to customization of hanger dimensions and material, giving flexibility in the casing system selection.

Expandables on wireline?
After developing the liner hanger, the project team set about upgrading the design of the downhole expansion tool, which had already been developed for use with internal and external casing patches.

Most significant was the design and build of a wireline-deployed hydraulics module. The electrically powered unit delivers the fluid power required to drive the downhole intensifier.
Table 1. HETS Liner Hanger Specifications.
The combination of the two delivers up to 29,000 psi of controlled hydraulic pressure to the expansion seal unit and monitors the expansion process in real time. Unfortunately the tool test program was not completed in time for the first operation, which was carried out on drill pipe, but the considerable operational timesaving provided by this deployment method will be available on the next well.

The wireline development also opens up an intriguing new set of options for solid expandable devices. This is of particular significance in the subsea well intervention environment.

The flexibility of HETS deployment options on wireline, coiled tubing or drill pipe offers optimized planning in the construction process. This is the first system to offer true expandable tubular solutions on wireline and coiled tubing, presenting the possibility of deploying systems into live wells. HETS offers new solutions that enable the slim well as a real alternative to the monobore well and presents alternative methods to extend the design envelope for deepwater and deep-well construction, giving TTRD and through tubing completion activities vital new tools in the design box. Wells can be designed with built-in flexibility to adapt dynamically to the construction process and all its unexpected challenges.