Expandable multizone completions in unconsolidated strata help lock sand in place, and new swellable packer technology helps achieve zonal isolation.

For many years, openhole completions consistently have delivered better performance than the cased, cemented and perforated alternative. However, historical uptake has been impeded by the inability to achieve effective zonal isolation. A field-proven expandable reservoir completion (ERC) system from Weatherford combines slotted and solid expandable technology and features a return to conventional unexpanded premium connections to deliver a freely configurable reservoir completion architecture, offering a combination of openhole production performance and cased hole isolation capability.
With more than 400 expandable sand screen (ESS) jobs performed worldwide, totaling more than 205,000 ft (60,975 m) of installed screen, the company has benefited from valuable experience that has led to new, improved designs. Among these is the new 81/2-in. ERC system that combines field-proven ESS technology with the expandable zonal isolation (EZI) system. This has paved the way for multiple-zone openhole completions with positive pressure isolation.
Not only do these new developments eliminate costly casing, cementing and perforating operations, but they also provide several advantages that improve well productivity and sand control effectiveness:
• The larger bore allows room for intelligent well systems and promotes a more even sweep across the production interval, delaying the onset of water or gas influx and delivering better overall return from the reservoir.
• The overall surface area of the completion is greater, thereby increasing the effective area open to flow and reducing the potential to plug the filter.
• Removing the need to perforate casing, which can create localized erosion nodes, eliminates premature screen failures.
• Expanding the sand screen against the formation provides wellbore contact, which in turn supports the sand grains ultimately promoting particle bridging.
New 81/2-in. ERC concept
The system has some unique characteristics. It is modular and uses premium threads, enabling easy integration with standard blank pipe sections and other zonal isolation systems.
Expandable sand screen. A new size of ESS, incorporating a 7-in., 29 ppf base pipe, has been created as part of the system. The 7-in. platform enables a greater range to ensure compliance in hole sizes in excess of 9.2 in. A thicker wall section and optimized slot pattern increase the strength of the product.
Unlike the original ESS design, the base pipe is not slotted along its entire length; solid pipe remains at the joint ends, to allow for non-expandable premium couplings. Unexpanded premium couplings and standard casing blank sections underlie the robust nature of the new product and are common to all system components, promoting modularity and integration with conventional oilfield technologies. The transition between the non-expanded and expanded section includes solid plates behind the weave to prevent potential erosion over the non-compliant length.
Expandable zonal isolation. The key to the system is the EZI device, which uses a proprietary, rotary-compliant expansion technique to clad the formation wall, affecting openhole zonal isolation.
The expandable section of the EZI unit features an extended section of molded, ribbed elastomer with solid end back-up (Figure 2). Elastomers are protected during deployment by cross-coupling centralizers, and a mechanical tag is located within the expandable section for positive depth correlation during expansion.
ERC expansion system. Both the ESS and EZI are expanded using proprietary, rotary-compliant expansion technology, and both require slightly different tool designs. The ESS has a larger percentage expansion requirement with reduced force. The EZI requires a lower percentage of expansion, but requires higher expansion forces. For this reason, two different expansion tools are required in the string. The ESS expansion tool is situated at the bottom of the string and incorporates two rows of three piston-mounted rollers. The EZI tool is situated above the ESS tool and has one row of piston-mounted rollers.
Diverter tool. Selecting the appropriate expansion tool for the zone requires a diverter tool to be incorporated in the string between the two tools. The diverter tool simply switches between the ESS and EZI tools using flow rate and associated backpressure.
The EZI units can provide an immediate seal up to a 3,000 psi (206.8 bar) differential pressure rating. In addition to this, the system also allows integration with other isolation media, such as swellable packers, and the use of standard 7-in. casing to span problem sections in the reservoir.
Swelling elastomer technology
The swell packer is manufactured and bonded directly onto any size base-pipe. Differential pressure depends on initial rubber thickness. The full limits of differential pressures can be modeled using empirically tested reference points.
The swelling process effectively degrades the mechanical properties of the elastomer. Therefore, pressure retention capability varies inversely with wellbore internal diameter. Swelling capability of the elastomer depends on wellbore fluid and temperature conditions. The life of the downhole seal has yet to be ascertained. The most developed product is designed to be run in oil. Although there are some products now being run in water and gas, the results are not yet fully qualified.
Proving the technology
Several tests of the system have been run in conjunction with BP as part of the joint project. The first in Wyoming last year, proved EZI isolation capability in openhole applications. The second, in a live gas well in south Texas, proved the combination of ESS and EZI systems and provided a pressure isolation of 1,450 psi (100 bar). Another injector installation in the Caspian Sea's Chirag field was completed using the ESS component only. The latest application was a dual-zone water injector in Alaska, using corrosion-resistant alloy (CRA).
In qualifying the 81/2-in. ERC system, BP has taken a stepped approach, first installing a multizone isolation in a gas producer, then only a single-trip ESS installation in a deviated injection well, followed by a dual-zone water injector using CRA.
Out of Africa
Working for Chevron in the Gulf of Cabinda, offshore Angola, the company set a world record for its 41/2-in. ESS system. At 2,500 ft (762 m), the Takula-18 (IS) well is the world's longest 41/2-in. ESS completion. The well was completed in a 61/8-in. openhole section at 60° inclination. Four zones were screened, using 41/2-in ESS systems and isolated using 57/8-in. swell packers. The operation was conducted in a single trip. A Weatherford EXR hanger/packer was hung off in the 7-in. liner at 5,726 ft (1,746 m), and the completion was deployed to 8,387 ft (2,557 m) measured depth (MD). The running tools were released from the hanger/packer, and the expansion string continued into the hole to expand the ESS portion of the completion. An axial-compliant expansion (ACE) tool was used to conform the screens to the hole profile. A total of 2,030 ft (619 m) of screen was expanded, and 51/2-in. blank pipe was used between the lower and upper screen sections to bridge across the water zone.
To address another challenge in West Africa, Weatherford is adapting its 51/2-in. ESS system to cope with multiple zones when using 7-in. base pipe for the swell packers and space-out between zones. This option was previously not possible because a 75/8-in. base pipe was required to allow pre-expansion of the system using a 65/8-in. fixed-diameter cone. The 75/8-in. base pipe limited the amount of swelling elastomer that could be applied while still allowing an acceptable running clearance. This limitation, in turn, restricted the pressure rating of the system, as the rating is directly proportional to the degree of elastomer swell.
Conclusion
Expandable sand screen technology has been widely adopted by the industry and has provided the knowledge platform from which to begin the shift towards this new concept in reservoir architecture. Until now, conventional wisdom held that unconsolidated formations with multiple producing zones should be completed cased hole, despite the negative impact on well productivity. Now, through the use of field-proven expandable technology, all the zonal isolation benefits of a cased and perforated completion are available with openhole productivity performance.

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